Siemens SINUMERIK 840D sl Function Manual page 55

Accuracy
If the programmed end point does not lie exactly on the involute defined by the starting point,
interpolation takes place between the two involutes defined by the starting and end points (see
illustration below).
The maximum deviation of the end point is determined by the machine data:
MD21015 $MC_INVOLUTE_RADIUS_DELTA (end point monitoring for involute)
Figure 2-7
Basic Functions
Function Manual, 01/2015, 6FC5397-0BP40-5BA2
MD21015 specifies the max. permissible deviation
A2: Various NC/PLC interface signals and functions
2.3 Functions
55