Summary

This 100mm circle serves several purposes:

1) The circular 'brim' shape is designed to be exactly 1 layer high. 0.1mm and 0.2mm versions are provided; be sure to use the appropriate version for your print settings.
To use it as a brim around your model, use a program such as TinkerCad, Microsoft 3D Builder, Cura, etc. to place your model inside the circle. Save the combined file, then print.
Customize these samples for other layer heights to test your printer's print quality across its entire layer height range.

2) You can use it to ensure that your printer is calibrated correctly.

3) Measure it to determine whether a 100mm circle prints larger or smaller than expected.

4) Observe that Delta printers print circles as a series of straight lines.