CIGAL Reference Manual, Chapter 0 (clock):
usage: dest = clock
or: clock = value
CLOCK is a number variable that counts the number of cycles of the computer's internal clock. The value of this variable is set at the moment it is read.
Assigning a value to CLOCK does not store that value in the CLOCK variable, instead it changes the way CLOCK reports the passage of computer time. The following gives the meaning of the assigned value:
0 - reset the CLOCK count to 0; subsequent values of CLOCK will be the number of computer clock cycles since this moment. VALUE > 0 - VALUE < 0 -