mxavier has a nifty tip for calc:
Tiny but nice #emacs TIL: in calc-mode, y will insert the current calculation into the buffer from which you called calc-mode.
— mxavier (@mxavier) June 12, 2015
It’s hard to put a lot of context into a tweet so let me fill in the blanks. If you’re in the calc buffer, typing【y】 (calc-copy-to-buffer) will copy the top of the stack to the most recently used editing buffer. The documentation clarifies that as
More specifically, this is the most recently used buffer which is displayed in a window and whose name does not begin with ‘*’. If there is no such buffer, this is the most recently used buffer except for Calculator and Calc Trail buffers.
This makes it easy to pop into calc, make some calculations, and then copy the result back to the buffer you were working in. Actually, calc-copy-to-buffer is a bit more flexible. You can read the Yanking into Other Buffers section of the manual to get the details. It’s short and well worth a look.