Cut and paste this URL to share the unmodified register and value:
https://regviz.com/r/STMicroelectronics/STM32L0x2/RTC/CALR#0x0
RTC calibration register
Calibration minus
Use a 16-second calibration cycle period
Use a 8-second calibration cycle period
Increase frequency of RTC by 488.5 ppm
https://github.com/cmsis-svd/cmsis-svd-data