We know that you want to see here one number, which is valid under any circumstances. But unfortunately, we cannot provide you this magical number.
There are many influence factors, like:
Number of used based stations
Calibration of the system (Origo, X, Y)
The surrounding room (sunlight yes, no), reflecting objects
Distance of the light boxes from the recording place
etc.
Please keep in mind: this is an optical system. The components were developed for gaming. So do not expect high end 3D laser measurement precision. As a tradeoff, you get a very affordable device which shorten the path creation time significant.
Our best practice values for the accuracy with 2 base stations are:
Standard: 2-3 mm offset
Well calibrated and precise setup: appr. 1mm offset