This Test Specimen is made of a 5x5mm square of single crystal silicon. It is photo-etched and the squares repeat every 10µm. The dividing lines are 1.9µm wide. A broader etching line is written every 500µm, which is useful in light microscopy.
The pair of dots, which appear to merge into a single dot, determines the amount of vibration of the slide in the appropriate axis. The pattern on the S25 is an array of 20 pairs of dots converging on a single dot.