If you use NickelMenu, you could use my typography script to display the current reading settings, and then you can verify that you put the sliders back to their original positions after you've done your testing. It would be nice if Kobo actually displayed numbers next to the sliders in the UI, but alas, we must come up with our own workarounds.
https://www.mobileread.com/forums/sh...postcount=1038