Clockes going back and digi tacho.

[jagracer]

I normally use an analogue tacho but have had a rental truck for a few weeks and have been using my digi card. The clock on the tacho has been an hour behind, which I have been told is normal. When I got in the truck today the clock read the correct time, it was 4am GMT and it read 4am so nothing had been altered. However at some point this morning the clock itself has jumped forward 1 hour so when I logged off at 11.30 the clock says 12.30. The tacho printout however gives the correct time saying I started at 4am and finished at 11.30. What's going on with this, I haven't altered any clocks in the truck or tacho so it wasn't my doing.
Any info would be welcome.

[jagracer]

Just noticed I spelt clock wrong.

[jagracer]

Thanks for all the replies, the lorry has gone back now and I'm back sticking a round bit of paper in tomorrow.