Hobbs.....hour meter which starts when the master goes on. Pay £40 per hour Hobbs time. Keeps it simple and leaves a bit in the pot to pay for the annuals, as most aircraft maintenance times are done by tachometer hours which, I believe, only start ticking up above a certain RPM or oil pressure or something like that.
You can pick up a quater for around £7000, or less. I paid a little bit more but the aeroplane had just been completely rebuilt, re-painted, new wings, corrosion proofed etc.....so it was effectively a new aeroplane.