by hdonk, published
After trying to determine if size problems of inner features on a print were caused by miscalibration of the X or Y axis steps per mm, I came up with this.
It allows the measurement of head move distances by looking at the spacing between voids - that way if there's over or under extrusion, the measurements are of the voids.
Print the test piece.
The square ends are the X axis. The round ends are the Y axis.
Find a matching pair of holes at each end of the piece, where the hole is only barely visible.
Measure the distance between the holes using a micrometer.
The distance should be 100mm. If it isn't, recalibrate the steps per mm on that axis.
Rinse and repeat.