Cut and paste this URL to share the unmodified register and value:
https://regviz.com/r/STMicroelectronics/STM32F030/RTC/CALR#0x0
calibration register
Calibration minus
Reserved
Use a 16-second calibration cycle period
Use an 8-second calibration cycle period
https://github.com/cmsis-svd/cmsis-svd-data