Add a key stroke command that toggles calculations on/off. Maybe Ctrl-Shift-x.
Turning calculations off is very handy to avoid Mathcad solving repeated changes (i.e. if you are changing 5 inputs it can solve 5 times, which can take some time for an advanced calculation.) Sure, calculations can be turned off with the mouse and menus - but that takes too long since I have to go to a tab, click it, inevitably go back to the Math tab, perform my updates, then back to calculation tab to turn it on. That's very inefficient and is often repeated multiple times.
Also, allow Auto Calculation/Stop All Calculations to be added to the quick access toolbar.