I noticed this question was raised 5 years ago but the thread is closed without discussion.
https://forums.stardock.com/470714
I too would love to use Start10 as a simple calculator, where I enter in "1+1" and the answer "2" appears/refreshes as I continue to add numbers and operators.
The default Windows 10 Start Menu only does this with Bing Search and telemetry enabled, and I was really really hoping Stardock Start10 would have this feature by default but it seems not (unless I've missed a setting, still very new to this app).
Cheers for hearing me out!