220mm single bed level calibration line

thingiverse

I use this single line strip to test the flatness of my adventurer 4 bed. I import 3 of these STLs into the print volume and put one in the front, one in the middle, and one at the back (90mm, 0mm, 90mm). Layer height doesn't matter too much (I use 0.24mm). How I determine if the bed is flat is by taking callipers and measuring the thickness along each of the lines after removing them from the bed.