https://devzone.nordicsemi.com/f/nordic-q-a/11301/using-app_timer-to-implement-rt-clock-calendarHi, In my application I need to keep both time and date so I need a real time clock &amp; calendar (RTCC). I was planning to use on the nRF51 real time counter (RTC) to implement my own RTCC, but RTC0 is used by the S110 and RTC1 is used by the app_timeren-USTelligent Community 13Wed, 13 Jan 2016 23:24:11 GMThttps://devzone.nordicsemi.com/thread/42507?ContentTypeID=1Wed, 13 Jan 2016 23:24:11 GMT137ad170-7792-4731-bb38-c0d22fbe4515:61497276-97b6-4fab-8fbd-b0be9d532b83RK<p>No real difference between using an app_timer and using a free RTC, which you are correct in this case you don&#39;t have as both RTCs are in-use. It&#39;s still interrupt-based, it still wakes up on a regular interval and increments a counter, doing it via app_timer instead of a dedicated RTC runs more code because the app_timer is reasonably complicated, but it&#39;s still basically pretty low power, especially if you&#39;re waking up often for bluetooth events to occur anyway.</p> <p>Accuracy may not be particularly great however, a few seconds a day of drift is possible. The RTCC chips also often provide calendar functions with rollover and leap years and useful stuff, so if that&#39;s important to you as well as low power, that might be another reason to use a separate chip.</p><div style="clear:both;"></div>