As indicated above, the time arithmetic functions are accessed in the
timer device structure as if they were a routine library. To use them, you
create an IORequest block and open the timer.  In the IORequest block is a
pointer to the device's base address. This address is needed to access
each routine as an offset - for example, _LVOAddTime, _LVOSubTime,
_LVOCmpTime - from that base address.

     Timer_Arithmetic.c 

 Why Use Time Arithmetic?