[kylecordes]

I'm not sure whether it is all that useful for a generic gauge display component to be accessible - rather, when using them an application author could probably make the overall application far more accessible than the gauge could itself ever be. The application using it has much more context with which to provide an alternative text based representation of the data, right?

[extra88]

In general, its better to bake accessibility in to a thing than to have a separate accessible version. If the gauge is the component for presenting this information, then it should present the information to all users.

My first thought is for the data to be in the HTML as a input type="range," with the readonly attribute and the value updated as needed by JavaScript. An additional ARIA live region attribute to offer guidance on when (or if) changes to the value should be announced would help. The canvas object could either get the range and current value from the input element or whatever JavaScript updates the input value also updates the canvas gauge. As someone else suggested though, SVG is probably a better choice than canvas.