Siemens SINUMERIK 808D ADVANCED Programming And Operating Manual page 73

Note
Further possibilities for circle programming result from:
CT - circle with tangential connection and
CIP - circle via intermediate point (see next sections).
Input tolerances for the circle
Circles are only accepted by the control system with a certain dimensional tolerance. The circle radius at the starting and
end points are compared here. If the difference is within the tolerance, the center point is exactly set internally. Otherwise,
an alarm message is issued.
Information
Full circles in a block are only possible if the center point and the end point are specified.
For circles with radius specification, the arithmetic sign of CR=... is used to select the correct circle. It is possible to program
two circles with the same starting and end points, as well as with the same radius and the same direction. The negative sign
in front of CR=-... determines the circle whose circle segment is greater than a semi-circle; otherwise, the circle with the
circle segment is less than or equal to the semi-circle and determined as follows:
See the following illustration for selection of the circle from two possible circles with radius specification:
Programming and Operating Manual (Milling)
73
6FC5398-4DP10-0BA1, 01/2014