I don't understand eeprom!

Hello!

Following this guide:

https://www.youtube.com/watch?v=tDLbqLve128&index=2&list=PLAwzSiNh9kbgxNy5E9O9Q_zOskIZ5wF7_

The guy uses extensive use of m500, m665 and m666.

I'm using marlin, and trying to dial in a mini kossel.

I'm failing at the first hurdle (I have eeprom enabled; #define EEPROM_SETTINGS //to disable EEPROM Serial responses and decrease program space by ~1700 byte: comment this out: // please keep turned on if you can. #define EEPROM_CHITCHAT).

However, I send a command for the x tower endstop offset, and it sends (m666 x2.7), I then send m500 to save, I home using g28 and then re run the positioning of the nozel / bed and still the distance using m114 is -2.7! Shouldnt the m666 have made that 0?

Is there something that I can test to ensure that eprom is working OK?

Maybe I should walk away for the evening!

Thanks