Oh, and telescopic bore gauges are a skill in their self, however when you need them, they are invaluable. Short of spending a huge amount of money on lots of three point micrometers, there's no other cost effective way of measuring various diameters of deep bores.
I've got a set, however I think I've only ever used them once in the past year, and that was to measure deep enough down a worn bore to get a starting measurement for a repair.