How can I check which firmware version is installed on my device?

The firmware version number is shown on the screen during the startup process of the device.

The firmware version number starts with a letter, followed by 2 or 4 digits.

Recent firmware versions always start with the letter S, followed by 4 digits. Example: S54-01
Older firmware versions start with the letter C, followed by 2 digits. Example: C36.