R&D notes

Designing an accessible calculator

Jonathan Robert Pool

A 2018 project to reimplement a popular calculator application on the web, with accessibility improvements.

Starting point

Compact electronic calculators came into existence in the early 1970s, and they have generally used buttons for the input of individual digits and operators. Calculator applications on devices with full keyboards have often used graphical interfaces emulating the original calculator appearance. For example, the Macintosh OS X Calculator, in basic mode, looks like this:

Macintosh Calculator

Examination of that application reveals some accessibility issues, including:

Design decisions

It is arguable that an accessible web-based calculator has no reason to look anything like the physical calculators that have been made since the 1970s. Perhaps they should be HTML forms with the most efficient input mechanisms for the terms and operators. The design problem may resemble that of faceted boolean searching for library resources. Such a design would permit users to make corrections anywhere in an entered string, not only backwards from the end.


The study project I undertook in 2018 ignored the possibility of a radical departure and retained the basic idea of a physical-like button-based appearance. Within that constraint, it sought to avoid some of the above-described accessibility problems. The resulting prototype is available for testing.

Here is an example of the appearance of the prototype during use:

accessible calculator prototype showing entire expression entered so far and irrelevant buttons dimmed

Improvements in accessibility

The prototype incorporates the following accessibility improvements:

Further work could investigate changes that would, among other things, improve nonvisual usability and accessible user control over rounding precision.