Consider the very top graph of the set of three, where I use the terms Amplitude, Distance and Length to describe the vertical axis. This is showing the change in distance per step. For example, looking at post 333, I an moving the stage in 0.1" increments. The Nano is showing it from 0.101" down to 0.042". That was using the home made phase trimmer.
Looking at post 334, where the stage is not moving, the change is +/-0.002".
Looking at post 335, where the home made trimmer was replaced with the Sage commercial part where I am adjusting it by hand, it shows between 0.224 and 0.271"
Post 336 was an attempt to do an A/B compare between the home made trimmer and the commercial part by stepping roughly the same amount. The was between 0.174
and 0.280".
Post 340, the stage is incremented by 0.01" (its really 0.01000976... as it is not an even divisor). The software reports a mean of 0.0103". The stage moves 150 steps and show move 1.501465" compared with the reported 1.5314". I zoomed into the side lobes to show the spacing and we can see they are not uniform.
The middle graph is just the histogram of the step sizes. Or how many times the step size falls into a bucket.
The trimmer is brass. Your local hobby shop should have all sorts of shapes and sizes to choose from. There is also McMaster Carr.