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?