The sub count register RSUBC counts the reference time for a one second interval. It counts up to 0x8000 (corresponding to 1 sec @ 32.768kHz) and then increments the Second Count Register by one and so on. Since sub-oscillator crystals are not that accurate and can have a wide drift over temperature range, Renesas has implemented a Watch Error Correction feature. The watch error correction value can be set depending on the temperature. This helps to improve accuracy of the real-time counter by offsetting the inaccuracy of the sub-system clock drift over temperature.