Numbers on Rear view mirror

on my 97 Chevy Silverado I have a power rear view mirror and if I hold down the Comp button it goes from what direction your are going to numbers and you can keep hitting it and it will go from 1-15 what is it? and also when I start up the truck it shows the 100* all the time like it could have a temp guage on it. but I am not sure how to activate that option or could not it never have it. Please help and thank for your time

The numbers 1-15 are magnetic variation calibration numbers for different geographic locations. Your Owners Manual should explain it in detail.