Sample of tool usage is in last part of video.
3d printer bed level gauge.
Home the z axis of your 3d printer.
If it homes to z max then send it to z 0 manually.
A piece of ordinary office paper cut down to about 100 mm x 40 mm should work.
For 3d printer bed leveling and nozzle gap adjustment you ll need a card of a size you can comfortably hold and slide between the nozzle tip and the build plate.
Now level the print bed the same way you do with paper.
Start by tightening down all the screws so you have more room to work with.
To actually level the bed is really simple it just takes some practice to get it right.
Move your extruder to a corner and position the blade under the nozzle adjust the screw until the led will light up indicating that the tip of the nozzle is touching the feeler gauge blade repeat the process in the other corners until you find the perfect calibration.
Connecting a multimeter in continuity mode causes a beep sound when the head is the correct distance.