Difference Between

Difference Between Arithmetic and Geometric

Nex Virox Team
Written byNex Virox Team
Editorial Team
Varshal Nirbhavane
Senior SEO & Organic Growth Professional · 5+ years
21 min read
Quick answer

The main difference between Arithmetic and Geometric is that Arithmetic sequences use a constant difference between terms, while Geometric sequences use a constant ratio. Arithmetic is adding or subtracting the same value each step, while Geometric is multiplying or dividing by the same value each step.

Key takeaways

  • Core distinction: Arithmetic sequences add a constant difference; geometric sequences multiply by a constant ratio.
  • How each works: Arithmetic growth stays linear, while geometric growth accelerates exponentially as terms progress further.
  • Performance impact: Geometric sequences outpace arithmetic quickly; after ten steps, geometric values dwarf arithmetic totals dramatically.
  • Best-fit use: Arithmetic suits fixed payments or salaries; geometric models compound interest, population growth, or depreciation.
  • Common mistake: Assuming linear arithmetic patterns apply to compounding scenarios that actually require geometric calculations instead.

Difference Between Arithmetic and Geometric: Comparison Table

AspectArithmeticGeometric
DefinitionSequence where each term differs from the previous by a constant, fixed amount called the common difference.Sequence where each term is multiplied by a constant, fixed ratio called the common ratio.
PurposeModels linear growth or decline where change happens by adding or subtracting a fixed quantity each step.Models exponential growth or decay where change happens by multiplying or dividing by a fixed factor each step.
Core MechanismUses addition or subtraction of a constant difference (d) to move from one term to the next term.Uses multiplication or division by a constant ratio (r) to move from one term to the next term.
General Formulanth term equals first term plus (n minus 1) multiplied by the common difference d.nth term equals first term multiplied by the common ratio r raised to the power of (n minus 1).
Common DifferenceDenoted as d; calculated by subtracting any term from the term that follows it in the sequence.Denoted as r; calculated by dividing any term by the term that precedes it in the sequence.
Growth PatternGrows or shrinks by a constant absolute amount each step, producing a straight-line graph when plotted.Grows or shrinks by a constant percentage each step, producing a curved exponential graph when plotted.
Rate of ChangeRate of change is constant and linear; the slope remains identical between every pair of consecutive terms.Rate of change is proportional to the current value; it accelerates or decelerates as the sequence progresses.
Sum FormulaSum of n terms equals n divided by 2 times the first term plus the nth term.Sum of n terms equals first term times (1 minus r to the n) divided by (1 minus r), provided r is not 1.
Term Growth SpeedTerms increase slowly and predictably; each term adds the same small or large fixed number.Terms can explode rapidly; multiplication compounds, so later terms dwarf earlier terms dramatically.
Zero and NegativeCan include zero and negative terms freely; the common difference can be any real number including zero.Cannot include zero terms if the ratio is nonzero; negative terms alternate signs only when the ratio is negative.
Graph ShapeProduces a straight line with a constant slope equal to the common difference d when plotted.Produces an exponential curve that rises or falls steeply depending on whether the ratio exceeds 1 or lies between 0 and 1.
Real-World ExampleSalary increasing by a fixed $2,000 each year, or saving a constant $100 monthly into a plain account.Population doubling every decade, or a bank balance growing by a fixed 5% interest rate compounded annually.
Computational CostComputing the nth term requires only one addition and one multiplication, making it extremely cheap to calculate.Computing the nth term requires exponentiation, which is slightly more expensive but still trivial for modern processors.
AccuracyPredictions remain accurate for long ranges because the constant difference never drifts or compounds errors.Predictions become highly inaccurate over long ranges because small ratio errors compound exponentially with each term.
ScalabilityScales linearly; doubling the number of terms roughly doubles the total sum without surprising jumps.Scales exponentially; adding a few more terms can multiply the total sum by a large factor quickly.
Data FittingFits datasets where successive differences between measurements remain approximately constant across the range.Fits datasets where successive ratios between measurements remain approximately constant, such as compound interest or radioactive decay.
Forecasting HorizonReliable for long-term forecasts because the linear trend continues predictably far into the future without compounding.Reliable only for short-term forecasts; exponential projections quickly become unrealistic beyond a few periods.
Inverse OperationReverse operation uses subtraction; finding the previous term requires subtracting the common difference d.Reverse operation uses division; finding the previous term requires dividing by the common ratio r.
Common Ratio ZeroNot applicable; arithmetic sequences have no ratio concept, only a difference between consecutive terms.If the ratio is zero, all terms after the first become zero, collapsing the sequence into a single nonzero value.
Negative RatioNot applicable; arithmetic sequences use addition, so negative differences simply decrease terms linearly.Negative ratios cause terms to alternate between positive and negative values, oscillating around zero indefinitely.
Financial ApplicationUsed for simple interest calculations where the same absolute interest amount is added each period.Used for compound interest calculations where interest is earned on previously accumulated interest each period.
Physical SystemsDescribes constant-velocity motion where distance increases by the same amount each second.Describes radioactive decay where the fraction of atoms remaining halves after each fixed half-life period.
Common MisuseOften wrongly applied to growth data that is actually exponential, producing severe underestimates of future values.Often wrongly applied to linear data, producing absurdly large or small predictions beyond the observed range.
Typical UsersUsed by accountants, payroll processors, and engineers calculating fixed incremental costs or linear depreciation.Used by financial analysts, biologists, and epidemiologists modeling compound growth, decay, or viral spread.
Educational ContextIntroduced first in algebra courses because the addition pattern is simpler for students to grasp intuitively.Introduced later in algebra or precalculus because exponentiation and ratio concepts require more mathematical maturity.
Sum BehaviourSum of n terms grows quadratically; doubling n roughly quadruples the total sum of the sequence.Sum of n terms grows exponentially; doubling n can multiply the total sum by a factor of r to the n.
Infinite SumInfinite sum diverges to positive or negative infinity unless the common difference is exactly zero.Infinite sum converges to a finite value only when the absolute value of the ratio is strictly less than 1.
LimitationFails to model compounding phenomena; linear assumptions break down when growth feeds on itself over time.Fails to model bounded growth; exponential assumptions break down when resources, space, or demand become limited.
Best-Fit ScenarioBest for fixed installment payments, straight-line depreciation, and any process adding a constant amount per period.Best for population growth, compound interest, viral spread, and any process multiplying by a constant factor per period.

What Is Arithmetic?

Arithmetic is the oldest and most basic branch of mathematics, dealing exclusively with numbers and the four core operations of addition, subtraction, multiplication, and division. It exists to provide the universal, reliable rules for counting, calculating quantities, and solving everyday numerical problems that all higher mathematics depends upon.

Definition of Arithmetic

Arithmetic is the branch of mathematics that studies numbers and the fundamental operations applied to them, specifically addition, subtraction, multiplication, and division, along with their properties such as commutativity, associativity, and distributivity. It forms the foundational layer for algebra, calculus, and all quantitative reasoning used in daily life and science.

Key Characteristics of Arithmetic

CharacteristicWhat It Means in Practice
Constant differenceAdding or subtracting the same fixed value repeatedly creates a predictable linear sequence of numbers.
Four core operationsAll arithmetic work reduces to addition, subtraction, multiplication, or division performed on concrete numerical values.
Commutative additionSwapping the order of two numbers in addition or multiplication always yields the exact same result.
Associative groupingRearranging parentheses in addition or multiplication does not change the final computed outcome.
Distributive propertyMultiplying a number by a sum equals multiplying it by each addend separately and then adding the products.
Exact, discrete resultsArithmetic operations produce precise, whole or rational values with no approximation or rounding required.
Zero and one identitiesZero acts as the identity for addition, while one acts as the identity for multiplication, leaving values unchanged.
Inverse operationsSubtraction reverses addition, and division reverses multiplication, allowing equations to be checked and solved.
Universal base systemArithmetic uses the base-10 positional system, where digit placement determines tens, hundreds, and thousands.
Order of operationsCalculations follow the standard PEMDAS rule: parentheses, exponents, multiplication, division, addition, subtraction.

Common Examples of Arithmetic

  • Grocery checkout – adding item prices and subtracting coupons to determine the final amount owed at the register.
  • Monthly budgeting – subtracting rent, utilities, and food costs from total income to find disposable savings.
  • Recipe scaling – multiplying ingredient quantities by a factor to double or halve a meal for more guests.
  • Time calculation – subtracting start time from end time to compute the duration of a commute or meeting.
  • Retail discount – multiplying the original price by a percentage and subtracting it to find the sale price.
  • Fuel efficiency – dividing total miles driven by gallons of fuel used to calculate miles per gallon.
  • Bank interest – multiplying a savings balance by the annual interest rate to estimate yearly earnings.
  • Brick wall layout – dividing wall length by brick width to determine the exact number of bricks required.
  • Classroom grading – adding all test scores and dividing by the number of tests to compute a final average.
  • Distance estimation – multiplying average speed by travel hours to estimate the total distance covered on a trip.

Advantages and Limitations of Arithmetic

AdvantagesLimitations
Arithmetic is universally understood across all cultures, languages, and educational systems worldwide.Arithmetic cannot model exponential growth, compound interest, or population booms without advanced functions.
It delivers exact answers, making it reliable for financial transactions, engineering measurements, and scientific counts.It fails to describe continuous phenomena like motion, curves, or changing rates that require calculus.
Basic arithmetic requires no calculators or tools, as simple mental math handles most everyday situations.Large or complex calculations become tedious and highly error-prone when performed manually by hand.
It provides the essential foundation for learning algebra, geometry, statistics, and all advanced mathematics.Arithmetic cannot represent abstract relationships, variables, or unknown quantities that algebra handles.
Arithmetic is fast to learn and apply, with most core skills mastered during primary school education.It offers no method for comparing ratios, proportions, or multiplicative relationships between different quantities.
It works with rational numbers cleanly, covering fractions, decimals, and integers without special cases.Division by zero is undefined, creating limitations in equations and real-world calculations that hit zero.
Arithmetic enables quick estimation, allowing people to approximate totals and verify reasonableness of results.It provides no way to express growth patterns where each step multiplies by a fixed factor, unlike geometric sequences.
It is deterministic and repeatable, meaning the same calculation always produces the identical result.Arithmetic struggles with irrational numbers like pi or square roots, which require approximation or rounding.
Arithmetic underpins coding, accounting, engineering, and construction, making it a practical career skill.It cannot solve problems involving repeated multiplication, such as compound growth, without exponential notation.
It builds logical thinking and problem-solving habits that transfer to broader decision-making scenarios.Arithmetic alone cannot handle probabilities, statistical variance, or data distributions used in modern analytics.

What Is Geometric?

Geometric is a sequence or series where each term is found by multiplying the previous term by a fixed, constant ratio. It models multiplicative growth or decay, explaining why it exists for compound interest, population expansion, and signal attenuation.

Definition of Geometric

Geometric refers to a sequence in which the ratio between any two consecutive terms remains constant, called the common ratio (r). This ratio is calculated by dividing any term by its immediate predecessor, and it governs the progression's multiplicative behaviour.

Key Characteristics of Geometric

CharacteristicWhat It Means in Practice
Constant ratioEvery term is the prior term multiplied by the same fixed number, never a different multiplier.
Multiplicative growthValues scale by factors, so growth accelerates or decays rapidly rather than adding evenly.
Exponential natureThe nth term formula uses the ratio raised to a power, producing curved, non-linear trajectories.
First term anchorThe starting value (a) sets the base, while the ratio dictates how fast terms move away from it.
Zero ratio limitA ratio of zero collapses all terms after the first to zero, ending the progression instantly.
Negative ratio flipA negative ratio makes terms alternate between positive and negative values with every step.
Fractional decayRatios between zero and one shrink terms progressively, modelling halving or percentage losses.
Sum convergenceInfinite geometric series sum to a finite value only when the absolute ratio is below one.
Log-linear formTaking logarithms of terms converts the pattern into a straight line for easier analysis.
Scaling invarianceMultiplying every term by a constant preserves the geometric property, keeping the ratio unchanged.

Common Examples of Geometric

  • Compound interest – each period multiplies the balance by a fixed rate factor, growing principal exponentially.
  • Bacterial division – one cell splits into two, doubling the population count at every generation step.
  • Radioactive half-life – a substance decays by half each fixed interval, a ratio of 0.5 per period.
  • Keyboard doubling – pressing a key doubles the displayed text, creating 1, 2, 4, 8 characters.
  • Paper folding – each fold doubles the layers, reaching 2, 4, 8, 16 thicknesses rapidly.
  • Chessboard grains – doubling grains per square yields 1, 2, 4, 8 up to enormous totals.
  • Sound intensity decay – each meter of travel reduces sound pressure by a constant percentage factor.
  • Depreciation value – a car loses 15% yearly, multiplying its worth by 0.85 each year.
  • Viral sharing – each person forwards a post to three friends, tripling reach per generation.
  • Musical octaves – each octave doubles frequency, so notes progress by a ratio of 2.

Advantages and Limitations of Geometric

AdvantagesLimitations
Models real compounding phenomena like interest and population with high fidelity.Fails when growth is additive, such as salaries or linear distance, producing wrong predictions.
Simple closed-form formulas allow instant term calculation without listing prior values.Extreme sensitivity to ratio errors means a small input mistake compounds into massive output divergence.
Infinite sums converge cleanly for ratios under one, enabling precise total calculations.Convergence fails entirely when the ratio equals or exceeds one, leaving sums undefined or infinite.
Logarithmic transformation linearises data, simplifying trend analysis and forecasting.Negative ratios create oscillating signs that misrepresent most physical quantities like counts or lengths.
Universally applicable across finance, physics, biology, and computer science domains.Assumes a perfectly constant ratio, which real-world systems rarely maintain over long periods.
Handles both explosive growth and rapid decay with the same underlying framework.Zero or undefined ratios break the sequence structure, leaving no meaningful progression to analyse.
Requires only two parameters, the first term and ratio, for full sequence specification.Cannot represent bounded growth like logistic population limits, where ratios change dynamically.
Enables quick comparisons of growth rates across different datasets via ratio values.Misleading for short-term projections because early terms look deceptively small before exploding.
Provides exact integer results when ratios are whole numbers, aiding verification.Fractional ratios produce unwieldy decimals quickly, complicating manual calculation and rounding.
Foundation for advanced concepts like geometric means and infinite series in calculus.Overestimates future values when applied to systems with capacity constraints or resource limits.

Similarities Between Arithmetic and Geometric

Shared AspectHow Arithmetic and Geometric Are Alike
Sequence CategoryArithmetic and geometric are both specific types of ordered number sequences in mathematics.
Core PurposeArithmetic and geometric both define a clear rule for generating each term in a sequence.
Input RequirementsArithmetic and geometric both require a starting term and a constant value to build the sequence.
Output FormatArithmetic and geometric both produce an infinite list of numbers as their primary output.
Mathematical BranchArithmetic and geometric both belong to the algebra and number theory branches of mathematics.
Term NotationArithmetic and geometric both use subscript notation to identify each term's position in the sequence.
Common VariableArithmetic and geometric both use the letter n to represent the term number or position in the sequence.
First Term RoleArithmetic and geometric both rely on the first term as the foundational starting point for all calculations.
Deterministic ProcessArithmetic and geometric both follow a fixed, predictable rule that produces the exact same sequence every time.
Recursive DefinitionArithmetic and geometric both can be defined by relating each term to the one that comes before it.
Explicit FormulaArithmetic and geometric both have a direct formula to calculate any term without listing prior terms.
Educational LevelArithmetic and geometric are both typically introduced to students in high school algebra courses.
Textbook CoverageArithmetic and geometric both appear as paired topics in standard algebra and precalculus textbooks.
Problem TypesArithmetic and geometric both appear in homework problems that ask students to find missing terms.
Calculator UseArithmetic and geometric both can be computed quickly using a standard scientific or graphing calculator.
Spreadsheet UseArithmetic and geometric both can be generated easily using formulas in spreadsheet software like Excel.
Real-World ModelsArithmetic and geometric both serve as mathematical models for describing patterns observed in real life.
Financial PlanningArithmetic and geometric both are used in finance to project future values of money over time.
Growth RepresentationArithmetic and geometric both represent how a quantity changes from one period to the next period.
Data AnalysisArithmetic and geometric both help analysts identify underlying patterns within collected data sets.
Prediction ToolArithmetic and geometric both allow users to forecast future terms based on past observed values.
Simple ComputationArithmetic and geometric both involve straightforward calculations that do not require advanced calculus skills.
Low Entry CostArithmetic and geometric both require no expensive software or materials to learn and apply.
Low Error RiskArithmetic and geometric both carry a low risk of calculation error when the constant value is applied correctly.
Verification MethodArithmetic and geometric both can be verified by checking that the constant difference or ratio stays consistent.
Pattern RecognitionArithmetic and geometric both train users to recognize regular, repeating numerical patterns quickly.
Logical FoundationArithmetic and geometric both build a logical foundation for understanding more advanced mathematical concepts.
Standard NotationArithmetic and geometric both use standard mathematical notation that is recognized globally by mathematicians.
Long-Term UtilityArithmetic and geometric both remain useful skills for careers in engineering, science, and data science.
Assessment FocusArithmetic and geometric both are common topics tested on standardized math exams and college entrance tests.

Arithmetic or Geometric: Which Should You Choose?

The deciding variable is how the change happens. Choose Arithmetic when the change is a fixed addition or subtraction. Choose Geometric when the change is a fixed percentage or ratio. Ask yourself: does the value grow by a constant amount, or does it grow by a constant rate?

When to Use Arithmetic

Choose Arithmetic when adding or subtracting a fixed amount matches your real-world pattern. Use it for simple budgets, monthly rent, or saving a flat $50 weekly. Arithmetic fits linear costs like salaries with fixed raises. It works when the gap between values stays identical every step.

When to Use Geometric

Choose Geometric when multiplying by a fixed ratio drives the change. Use it for compound interest, population growth, or viral content shares. Geometric fits depreciation at a constant percentage, like a car losing 15% yearly. It works when each step is a percentage of the previous value.

Common Misconceptions About Arithmetic and Geometric

Common MythThe Reality
Arithmetic sequences only ever involve addition, never subtraction.Arithmetic sequences use a constant difference, which can be negative, so subtracting a fixed value creates a valid arithmetic sequence.
Geometric sequences always grow larger with each new term.Geometric sequences multiply by a common ratio; if that ratio is between zero and one, every term gets smaller.
Arithmetic and geometric sequences are completely unrelated concepts.Both arithmetic and geometric sequences are ordered lists of numbers defined by a constant operation applied repeatedly to generate successive terms.
You can identify a geometric sequence by looking for multiplication signs.A geometric sequence is defined by a constant ratio between consecutive terms, not by the presence of multiplication symbols in notation.
An arithmetic sequence always has a positive common difference.Arithmetic sequences can have zero or negative differences, producing constant sequences or sequences that decrease steadily with each step.
Geometric sequences always involve whole numbers and integers only.Geometric sequences can use any real number as the common ratio, including fractions, decimals, and irrational numbers like the square root of two.
Arithmetic means finding averages, while geometric means drawing shapes.In sequences, arithmetic refers to a constant difference between terms, while geometric refers to a constant ratio, not geometry shapes.
Every sequence with increasing numbers must be geometric.An increasing sequence could be arithmetic with a positive difference; geometric growth requires multiplication by a ratio greater than one.
Geometric sequences are always faster growing than arithmetic sequences.Geometric sequences with a ratio between zero and one shrink, while arithmetic sequences with a positive difference always grow steadily.
Arithmetic sequences have no real-world applications beyond school math.Arithmetic sequences model constant payments, taxi fares per mile, and salary increments, making them essential for budgeting and financial planning.
Geometric sequences only appear in theoretical mathematics textbooks.Geometric sequences model population growth, radioactive decay, loan interest, and depreciation, so they appear constantly in finance and science.
The common difference and common ratio are interchangeable terms.The common difference is added in arithmetic sequences, while the common ratio is multiplied in geometric sequences; they are never interchangeable.
Arithmetic sequences cannot start with a negative number.Arithmetic sequences can start with any real number, including negatives, and still follow the rule of a constant added difference.
Geometric sequences must have a common ratio greater than one.Geometric sequences can have ratios equal to one, between zero and one, negative, or zero, each producing distinct and valid term patterns.
Finding the nth term is equally easy for both sequence types.The nth term formula for arithmetic uses addition of the difference, while geometric uses exponentiation of the ratio, making geometric harder for large n.
Arithmetic sequences always produce straight lines when graphed.Arithmetic sequences graph as discrete points lying on a straight line, but they are not continuous lines since only integer term positions exist.
Geometric sequences always produce exponential curves when plotted.Geometric sequences with a ratio between zero and one produce exponential decay curves, not growth curves, when plotted on a graph.
Zero can never be a term in an arithmetic sequence.Zero can appear in an arithmetic sequence if the starting term and common difference combine to produce zero at some position.
Geometric sequences never contain zero as a term.Geometric sequences can contain zero only if the starting term is zero or the common ratio is zero, which makes later terms zero.
Arithmetic sequences are always linear, so they are boring and useless.Arithmetic sequences model constant-rate phenomena like simple interest and uniform motion, which are fundamental in physics and economics.
Geometric sequences are always more complex than arithmetic sequences.Geometric sequences with a ratio of one are constant and trivial, while arithmetic sequences with large differences can be harder to compute mentally.
You need a calculator to solve any geometric sequence problem.Simple geometric sequences with small integer ratios and low term counts can be solved by repeated multiplication without any calculator.
Arithmetic sequences only use addition, so they cannot model decay.Arithmetic sequences with a negative common difference model steady decay, like a leaking tank losing a fixed amount of water each minute.
Geometric sequences always have a larger sum than arithmetic sequences.Geometric sequences with a ratio less than one can have a finite sum, while arithmetic sequences with nonzero difference always sum to infinity.
The difference between terms in arithmetic is always a whole number.The common difference in an arithmetic sequence can be any real number, including fractions like one-half or decimals like 0.25.
Geometric sequences always have a ratio that is a whole number.The common ratio in a geometric sequence can be any real number, including fractions, decimals, and irrational values like pi divided by two.
Arithmetic sequences cannot model compound interest growth.Compound interest follows a geometric sequence, while simple interest follows an arithmetic sequence, so each models different financial products.
Geometric sequences only apply to money and finance problems.Geometric sequences apply to biology for cell division, physics for wave attenuation, and computer science for algorithm complexity analysis.
Arithmetic and geometric sequences produce identical results for small numbers.Even with small starting values, arithmetic and geometric sequences diverge quickly because addition grows linearly while multiplication grows exponentially.
Knowing one sequence type means you automatically understand the other.Arithmetic and geometric sequences use different formulas, different growth patterns, and different sum calculations, so each requires separate study and practice.

Conclusion

Difference Between Arithmetic and Geometric lies in progression: arithmetic adds a constant difference, geometric multiplies by a constant ratio. Pick arithmetic for steady, linear growth. Pick geometric for exponential, compounding growth. Your choice depends on whether you need predictable increments or multiplicative expansion.

FAQs on Difference Between Arithmetic and Geometric

What is the basic definition of an arithmetic sequence?
An arithmetic sequence is a list of numbers where the difference between any two consecutive terms is always the same constant, such as adding 3 each time in 2, 5, 8, 11.
What is the basic definition of a geometric sequence?
A geometric sequence is a list of numbers where each term is found by multiplying the previous term by a fixed, non-zero number called the common ratio, like doubling in 3, 6, 12, 24.
What is the main difference between arithmetic and geometric sequences?
Arithmetic sequences grow by adding a constant difference, while geometric sequences grow by multiplying by a constant ratio, which makes geometric growth far faster over time.
Which is better for long-term growth, arithmetic or geometric?
Geometric growth is better for long-term expansion because multiplication compounds over time, whereas arithmetic growth only adds a fixed amount each step and cannot accelerate.
Which type of sequence carries more financial risk, arithmetic or geometric?
Geometric sequences carry more financial risk because their exponential nature can lead to rapid, unpredictable losses or gains, while arithmetic sequences change at a steady, predictable rate.
Are arithmetic and geometric sequences compatible with each other in one formula?
No, arithmetic and geometric sequences are not compatible in a single standard formula because one relies on addition of a constant while the other relies on multiplication by a constant, requiring separate equations.
What is a common beginner mistake when identifying these two sequence types?
A common beginner mistake is checking if numbers increase without verifying whether the change is a constant addition or a constant multiplication, which leads to mislabeling the sequence type.
Can an arithmetic sequence be used interchangeably with a geometric sequence?
No, arithmetic and geometric sequences cannot be used interchangeably because they model fundamentally different growth patterns, so swapping them would produce incorrect predictions for the same data set.
What is a real-world use case for an arithmetic sequence?
A real-world use case for an arithmetic sequence is calculating the total cost of renting equipment at a flat daily rate, where each additional day adds the same fixed fee.
Can I switch from an arithmetic to a geometric model for my data?
Yes, you can switch from an arithmetic to a geometric model, but only if your data shows a constant percentage change rather than a constant absolute change, otherwise the geometric model will be inaccurate.