I got to know that STM32F407VGT6 has an internal RTC support with either internal oscillator or an external one. Since the internal 32kHz oscillator is not that accurate, I would like to use an external 32kHZ oscillator. But I'm confused about the accuracy of the internal RTC with an external 32kHz crystal. Can I use internal RTC for date time keeping for logger applications? How many seconds do we lose in a year? Do I have to use the external chip (such as PCA8523, DS3231) for this?