Progress and numeric changes should be designed proportionally, not only absolutely
Aliases: proportional change · progress feedback · numeric change
What it is
For progress and numeric feedback to be visually noticed in time, consider proportional change relative to its reference, rather than applying one fixed absolute increment at every scale. Weber's law explains why a small segment at the end of a long progress bar, or one added to a large number, may be less conspicuous than the same early change.
Why it happens
Visual encodings such as length, area, brightness, and type size have detection thresholds. As a completed amount or reference value grows, a fixed pixel or numeric increment becomes a smaller proportion. Users who do not read every value may feel that nothing moved. Relative mapping or redundant markers counteracts this asymmetry.
Studying it
At several starting progress and number ranges, compare fixed increments, proportional increments, and text-assisted variants. Measure first-notice time, reading accuracy, and perceived continuity. For long tasks also measure waiting expectation and trust, since users judge whether the system is working as well as whether it changed.
Where it stops holding
Progress must honestly represent interpretable work; it cannot be exaggerated or made non-linear merely to appear active. Some values require absolute units, with proportional encoding as a supplement. Overly salient frequent changes can interrupt the main task, so prominence must fit importance.
Applying it
- For wide-range data, pair absolute value with percent and recent increment so people can read it and see its trend.
- For long waits, show stages, estimates, or an activity indicator rather than relying on subtle bar movement to prove liveness.
- Test when people notice updates at actual duration and screen size, and check whether salient feedback interrupts the primary task.