The time delay from the input (IN) of the DS1023 to the output (OUT) has two parts: 1. The component's inherent transmission delay and 2. The programmed delay. The time delay from the input (IN) to the REF output of the DS1023 is the inherent delay, so if we compare REF and OUT, the time delay here would be the programmed delay. From this comparison we can know, and hence eliminate, the error within the component itself.