This is a single layer vernier pattern printed on the build plate to calibrate X-scale, Y-scale, and Skew. The intent of the model was to make a calibration print that was large, could be printed very quickly (usually about 5 minutes or less), and used negligible material (only a few cm.)

The print uses a vernier pattern which is measured directly on the build plate instead of printing an object and measuring with calipers. The accuracy of the measurement is +/-0.005" (about +/- 0.1mm) over a span of 8" (about 203mm), so the overall accuracy is about +/-0.06%. That should translate to about +/-0.01mm over a 20mm object. Although some may not be satisfied with that accuracy, it's good enough for me considering how quick and easy it is to make (and verify) adjustments.

If you're not familiar with using a vernier pattern, I recommend looking it up. It's a remarkably simple way to make extremely accurate measurements "by eye" (although the tradeoff is that it requires a pattern that spans several marks that can be easily distinguished.)

I'm in US, so the scale I had on hand that was of trustworthy accuracy was an engineers drafting scale (German made) graduated in inches and tenths of inches. So, the primary dimension between the long marks is 8.000", and the shorter vernier marks are at 0.095" intervals (i.e. 0.005" per 0.100" mark.)

The reason that the print is in one continuous line (requiring zig-zags to create the measurement marks) is to make it very simple to remove the pattern from the build plate after making measurements.

If there is interest, I will gladly rework the model for smaller build plates and/or mm graduations.