Siemens SINUMERIK 840Di Function Manual page 37

Programming
A general description of involute programming appears in:
References:
/PG/ Programming Guide, Basics
In addition to the programmed parameters, machine data are relevant in two instances of
involute interpolation; these data may need to be set by the machine manufacturer/end user.
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 endpoint is specified by:
MD21015 $MC_INVOLUTE_RADIUS_DELTA
Fig. 2-7
Various NC/PLC Interface Signals and Functions (A2)
Function Manual, 08/2005 Edition, 6FC5397-0BP10-0BA0
MD21015 specifies the max. permissible deviation
Detailed Description
2.2 Functions
2-25