The title for this blog can be a bit misleading but let me assure that all these three things have something in common. The RTC clock allows you to measure real time and by assumption this measurement should be very precise. And the key word is assumption because depending on what kind of clock source you will chose you can get completely different results. All of it is dependent on the clock source, thus the internal oscillator. Additionally, since RTC shares the same special register space I will also discuss so-called backup registers. Let us get started.