Implement a built-in calculator in web app

[dtinth]

Sometimes I have to calculate some maths when deciding on pay amount for each person. It would be great if I can do this without having to switch to the calculator app.

Therefore, having a calculator right inside the app would make the app even more convenient! It can be as simple as a dialog box that asks user for a JavaScript or math.js expression. But also some innovative interfaces are encouraged. Just make sure it’s very easy to use on a mobile device.

If you want to help, please reply with a proposed design before submitting a PR!