How many significant figures?
Retina, 29 27 bytes
Saved 2 bytes thanks to @MartinEnder
^0\.0*.|^\d(\d*?)0+$
1$1
\d
Try it online! | Test suite
Saved 2 bytes thanks to @MartinEnder
^0\.0*.|^\d(\d*?)0+$
1$1
\d
Try it online! | Test suite