HowTo video.
https://rumble.com/vbbee5-prusa-3d-printer-mk3-heatbed-flatness-level-check-and-fix.html
Is your Prusa mk2 mk3 mk3s heatbed flat? Use this simple file to check. It’s a 1 layer .200mm think sheet that covers most of the heatbed. If you check the heatbed with some kind of strait edge make sure you do it when the heatbed is as printing temperature. My MK3 and two MK3s all were not flat when at printing temperature.
This is what I use for a straight edge. Make sure to inspect it to make sure it's got a good flat edge before purchasing.
https://www.walmart.com/ip/Best-Look-12-In-Paint-Shield-Trim-Guide-PS2-DIB/44105262
Here's the springs.
https://www.mcmaster.com/1986K79/
PLA or PETG
0.200mm layer
Use a nice slow speed for this print to make sure speed isn't a factor in the results. For PLA I use 20mm/s PETG 15mm/s.
The author marked this model as their own original creation.