Axis Baselines: Meaning Over Style

A quiet thought on something easy to overlook in business charts: the axis baseline — and why baseline choice affects truthfulness.

In many charts, the axis baseline is chosen arbitrarily — without due thought — often adjusted “to make the pattern clearer”. But the starting point isn’t a style choice — it carries semantic meaning.

A step back to how meaning is encoded in charts

Beneath every quantitative chart lies an underlying form: all such charts express value as a distance from a benchmark — whether that benchmark is zero (implicit for absolute quantities) or another reference such as an indexed benchmark, a target, or a defined reference. Intuitively, that benchmark is visually represented as the axis baseline.

Values shown in a chart can take two forms — absolute quantities or relative comparisons — and each requires a different baseline.

Absolute quantities

For charts showing absolute quantities — values understood through their distance from zero and whose magnitude is meant to be compared directly (whether expressed as units, currency, headcount, or percentage values such as year-on-year growth or margin) — the implicit benchmark is zero, and therefore the axis baseline should be zero.

A short clarification on YoY growth

Although YoY growth is derived from a comparison, the resulting percentage is an absolute quantity. Its magnitude is interpreted as distance from zero (“no change”), so its baseline is zero rather than a benchmark line.

Relative comparisons

For charts showing relative comparisons — where the value represents the distance from an explicit benchmark — the axis baseline should be that benchmark. The benchmark may be an indexed benchmark, a target, or any defined reference. Where helpful, the IBCS reference indicator can be used to make that reference explicit and unambiguous.

The above rule for relative comparisons should not be confused with cases where both the measure and the benchmark are shown as values. In those situations, they are absolute quantities and follow a different baseline rule.

A brief note on variance charts

A variance is a single absolute number (e.g. +7 or –3), but its meaning is inherently relative — it expresses the deviation from a benchmark.
In a variance chart, the zero line is not an absolute zero; it is the benchmark normalised to zero — an indexed reference line.
The bars show distance from that indexed benchmark, not from an absolute quantity baseline.

Showing measures and the benchmark together

When both the measure and the benchmark are shown as values (e.g. Actual 92%, Target 95%), they are absolute quantities and should use a zero baseline — except in cases where the measure has a true upper bound (such as 100% for accuracy or completion rates).
In those situations, the upper bound can serve as a legitimate baseline because it represents a meaningful reference point.

Where the benchmark is a single defined reference, the appropriate IBCS reference indicator should be used for clarity.

Why the baseline matters

When the starting point becomes arbitrary, the chart may look clearer, but the meaning becomes less truthful — small changes can appear dramatic, stable performance can look volatile, or the reverse.
The visual no longer reflects what the numbers actually mean.

If a zoom-in is needed to see detail, it is usually better to change the visual form — for example using a variance chart — rather than shift the axis baseline. Meaning stays intact, and the chart remains honest.

For a quantitative chart to be truthful, it must reflect what the data means; otherwise the visualisation loses its purpose and slips into data decoration rather than communication.

Visualisation should show meaning.
Axis manipulation disguises it.