This program is an easy to use calculator that follows significant figure rules.
Run it at https://xin-xin.me/code/sigfig/
It uses my tools (https://github.com/xinxinw1/tools) and prec-math (https://github.com/xinxinw1/prec-math) modules.
Download a local version by going to https://github.com/xinxinw1/sigfig/releases