Chart Scaling: Linear vs Logarithmic
The same price history can tell two opposite stories, and the only thing that changes is the vertical scale. Linear scaling gives every dollar the same height; logarithmic scaling gives every percent the same height. Pick the wrong ruler and a chart will happily exaggerate what does not matter and hide what does — before you have analyzed anything at all.
The Ruler Behind Every Chart
A scale is the ruler the chart draws with: the rule that converts price levels into screen height. Linear uses a ruler with fixed markings — every step is one dollar, forever. Logarithmic uses a ruler that stretches as the price grows — every step is one percent of whatever the price already is. Same data, two rulers, two different pictures.
None of this changes the data. Every trade, every close, every high and low stays exactly where it is. The scale only decides how distances look, and since chart reading runs on distances, the ruler quietly decides what looks big, what looks calm, and what looks like a trend at all.
Linear: Equal Steps, Equal Dollars
The linear scale, the default on nearly every platform, makes equal vertical distance mean equal dollars. A move from 10 to 20 draws exactly as tall as a move from 1,000 to 1,010: both are ten dollars, so both get the same height, even though the first doubled the price and the second moved it one percent.
For short ranges and quiet markets, that is perfectly fine: when the price lives between 98 and 105, dollars are dollars and the linear ruler is honest. The trouble starts when a chart spans a wide range, a decade, a growth stock, a whole bull market. Then the cheap years flatten into a featureless floor and the recent years tower over everything, purely because the price number got bigger.
Logarithmic: Equal Steps, Equal Percent
The logarithmic scale — log scale, in every charting menu — makes equal vertical distance mean equal percentage change. On it, a move from 10 to 20 draws the same height as a move from 1,000 to 2,000: both doubled, both are 100 percent, both get the same step.
That is the ruler traders who study long histories actually want, because returns compound in percentages, not in dollars. A chart that doubled twice over ten years shows two identical steps on log scale, the growth story reads at a glance. On linear, the same history shows one small bump and one towering climb, as if the early decade barely happened.
When the Wrong Ruler Lies
Each scale distorts, just on different horizons. Linear lies over long ranges: it buries early history, exaggerates recent moves, and can turn a steady percentage trend into what looks like a parabolic blow-off, or hide a real one. Log lies over short ranges, subtly: on a chart spanning a few dollars, the log ruler bends distances in ways that make small moves look smoother and more symmetric than they traded.
The classic mistake is judging a long uptrend on a linear chart: the price looks like it exploded recently, when in percentage terms the pace never changed. The mirror mistake is staring at intraday charts on log scale, where it adds nothing. Same data, two stories. The ruler decides which one you see.
Concrete case, round numbers: a stock that closed at 20, then 40, then 80, then 160, a clean doubling every year. On a log scale that history is four evenly spaced steps, and the steady pace is obvious. On a linear scale the same four closes draw a tiny bump, a medium step, and a towering leap, as if growth arrived only in the final year. Nothing about the company changed between the two drawings. Only the ruler did.
Which Scale, When
| Situation | Use | Why |
|---|---|---|
| Short range, small price span | Linear | Dollars are comparable; log adds nothing |
| Long history, big trend | Logarithmic | Percentages compound; early years stay visible |
| Judging growth pace | Logarithmic | Steady slope = steady percentage growth |
| Entries and stops on intraday | Linear | You act on dollars, not percent |
The professional habit costs nothing: on any long-term chart, check both. If the trend looks different on each ruler, the difference itself is information, and the reading that survives both scales is the one worth trusting. Scale is presentation; chart reading is substance, and the two skills stack.
Questions About Chart Scaling
Does switching the scale change my data or orders?
No. The scale is presentation only — prices, fills, and history are untouched. It changes what distances look like, nothing else.
Why do platforms default to linear?
Because it is the simplest ruler and works well on the short ranges most screens open with. The default is a starting point, not a recommendation — long-term charts deserve the switch.
Do professional traders use log scale?
On long-term analysis, commonly yes — it is the standard for multi-year charts precisely because returns compound by percentage. On intraday charts, most stay linear.
Should I measure my results in dollars or percent?
Percent, always, the same habit that makes log scale the honest long-term ruler. A 10-dollar gain means everything on a 12-dollar stock and almost nothing on a 1,200-dollar one.
Scale is the last piece of chart mechanics, the reading itself starts in reading a basic price chart, and the long trends these scales draw are the territory of bull and bear markets.