Siemens SINUMERIK 840D sl Programming Manual page 62

Parameter description
2.1 Parameter concept of the measuring cycles
Data display
The data in the operating area "Parameters" can be displayed by means of "User data",
"Global user data", "GUD..." or "Channel-specific user data", "GUD...".. As an alternative,
parameters that are not assigned values in the program or in the measuring cycles support
can be assigned values directly by experts.
Internal parameters
Measuring cycles also require internal parameters for calculations. Local User Data
(abbreviated to LUDs) are used in the measuring cycles as internal arithmetic parameter.
These are set up in the cycle and exist only during runtime.
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Programming Manual, 03/2009 Edition, 6FC5398-4BP10-2BA0
Measuring cycles