I hacked the code of the app and added a ruler option, I'll use Omnitrix as an example lol:
Original Omnitrix (Original app): by Azmuth (kenmaz)
Ultimatrix (My version of the app): by Albedo (Me)
Just kidding I didn't hack anything, I just wanted to use some ben 10 references 😅

In short: I made a normal square with 20 pixels pencil and spent half an hour making it look like a perfect square with 1 pixel rubber