Siemens sinumerik 840D sl Function Manual page 773

Boundary conditions
3.2 Boundary conditions for standard functions
Contour deviations are always generated if tool radius compensation produces contour
elements that are non-linear or circular. For example, G450 DISC=x, where x > 0 produces
parabolic or hyperbolic contour elements.
You will find a complete description of tool offsets in:
References:
/FB1/ Function Manual for Basic Functions, Tool Offset (W1)
38
Special functions: Retrace Support (TE7)
Function Manual, 11/2006, 6FC5397-2BP10-2BA0