I have that chain checker, it's brilliant

I've been keeping track of the wear on the drivetrain, but just casting an eye over the jockey wheels, and since the teeth aren't excessively worn I haven't thought about replacing them until now. The sideways play was quite a lot - but I kind of suspect I at some point may have cannibalized some parts from another bike... My commuter bike is sort of put together from the odds and ends leftover from other bikes

Anyway. New jockey wheels it is. But the shifting is already better.