I got myself a cheap ST Nucleo-L053R8 on discount, to play around with a couple ideas.
The main STM32L053R8 only has a low-frequency 32.768 kHz crystal for RTC, but it can also be provided with an 8 MHz clock from the included ST-Link USB programmer. The LF crystal is marked
32G501, and the ST-Link's is marked
Does anyone have any idea how accurate these two crystals are at room temperature? The documentation doesn't seem to specify.