Hyperglide!?

Wow! I didn't realise there was so much to a rear cassette.
I noticed a few weeks back that the teeth on the cassette of my new bike weren't all nice and uniform.
At first glance it looks like someone's made a right mess of shaping the teeth.
If you delve a bit deeper though you realise they're all carefully designed to help shifting up and down - Hyperglide - amazing stuff!

Anyway, bike fixed :-)
I mentioned my 'gears changing all by themselves problem' to the office bike guru and 5 minutes later the problem was solved.
That 5 minutes included explaining all about it and travelling down 6 floors to the basement car park!
Seriously, he just walked up to the bike, rotated a thumbscrew half a turn and that was it :-)