Eyeball it, you measure from which ever part of the stand moves the most.
Or math it. From center of the base to a corner is 2.24cm. If it spins about its center, it makes a circle with a circumference of ~14cm (2 * pi * r, where r is 2.24).
So: a 90 degree spin is 3.5cm, 180 degree is 7cm, etc.