Reducing number entry errors:
solving a widespread, serious problem

Example user interface

Harold Thimbleby
Swansea University
and Paul Cairns
York University
Head shot of Harold Thimbleby Head shot of Paul Cairns

Safer number entry demonstration

Most number entry systems (such as calculators and drug infusion systems) ignore keying errors and may confuse users. The demonstration here shows how a clearer number entry system might work, preventing many keying errors that are usually ignored. The demonstration also provides clear error messages.

See “Please don’t sleep through this wake-up call” (2001) for an example of the dangers of misreading numbers, which this demonstration seeks to avoid. The story there sees the rules of clear number-writing as applying to written numbers only. In this demonstration, we show how the rules can be applied to safer number entry systems, not just for handwriting.

Compare the safer number entry system here with the problems of a typical conventional calculator here.

The International Campaign to Eliminate Use of Error-Prone Abbreviations

The interactive demonstration (use it on this web page) avoids the serious problems highlighted in an internationally-approved PDF list, which despite being a national campaign supported since 2006 by both the U.S. Food and Drug Administration and the Canadian Institute for Safe Medication Practices has been ignored by device manufacturers. The interactive demonstration on this page shows how the FDA/ISMP rules could be put into any interactive device to reduced undetected errors.

The interactive demonstrator...

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Tick to try a variant keypad design.


Tick to show exactly what user keyed, so the user can see their last key error in detail. Uncheck this box so numbers displayed are always valid, but the last key pressed may not be shown if it causes an error (such as a second decimal point). If the display always shows valid numbers, the user may not know exactly what they mis-keyed.


Tick to use a red/green two-color background for the display. If the display is green, the number is valid so far (though it may not be when the user tries to enter it); if the display is red, the number is invalid.


Important details not demonstrated

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