HEIDENHAIN TNC 640 (34059x-05) ISO programming - Manual (Page 294)

Programming: Q Parameters
9.1 Principle and overview of functions
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TNC 640 | User's ManualDIN/ISO Programming | 1/2015
Programming notes
You can mix Q parameters and fixed numerical values within a
program.
Q parameters can be assigned numerical values between
–999 999 999 and +999 999 999. The input range is limited to
16 digits, of which 9 may be before the decimal point. Internally the
TNC calculates numbers up to a value of 10 10 .
You can assign a maximum of 255 characters to QS parameters.
The TNC always assigns some Q and QS parameters
the same data. For example the Q parameter
Q108
is always assigned the current tool radius, see "
Preassigned Q parameters", page 339.
The TNC saves numerical values internally in a binary
number format (standard IEEE 754). Due to this
standardized format some decimal numbers do
not have an exact binary representation (round-off
error). Keep this in mind especially when you use
calculated Q-parameter contents for jump commands
or positioning movements.