Comparing different stylus to sphere origin

I don't understand when I measure (not calibrate) the calibration sphere with a 2mm stylus and set the origin to 0,0,0 then measure the sphere with a 1mm stylus and the origin is NOT 0,0,0 but measures
0.05, 0.19, .003
I will use another stylus for example a 3mm stylus and the result may be .24, .114, .131, but the diameter is always correct.
All stylus have been calibrated prior to these measurements. The reason I'm concerned is that in some of my programs we have to change tips.