Problem
I have never been a big fan of the using a piece of paper under the nozzle to tram different spots on the bed and I have always wanted to quickly just know the difference in height at each bed screw. I have a BLTouch installed so there has to be a better way.
First solution
I started off by using an OctoPrint macro plugin to move the head to screw positions and then use G30 to probe the distance. This was helpful but the feedback was spread over many response messages and I would have to work out the offset relevant to a particular screw. Doable but a bit to much hunting for values and maths in my head.
Best solution so far
Then I found G35 Tramming Assistant in the marlin firmware.
I recompiled my firmware after updating these definitions:
#define ASSISTED_TRAMMING
#define TRAMMING_POINT_XY { { 31, 31 }, { 271, 31 }, { 271, 271 }, { 31, 271 } }
#define REPORT_TRAMMING_MM
Now when I run G35 all screw positions are probed and I get a simple readout like:
Turn Front-Right CW by 0 turns and 3 minutes (-0.0300mm)
Turn Back-Right CCW by 0 turns and 6 minutes (0.0525mm)
Turn Back-Left CW by 0 turns and 6 minutes (-0.0550mm)
Simple, easy to follow and saves me some brain cycles.