http://www.pprune.org/forums/showthr...5&pagenumber=3
Read page three of my old thread. There are some thoughts, not facts on tacho times. It seems to be generally accepted that 1.0 on tacho = 60 minutes at roughly cruise rpm, and that tacho records slower at slower rpm settings.
Also bear in mind that Hobbs meters generally record in increments of 0.1 (6minutes) whereas tachos record 1/100ths of an hour, so what you pay for vs what you fly, is far more accurate. It always used to annoy me when renting club aircraft that sometimes as soon as you started the engine, the hobbs would increas by 0.1 thereby costing me £9.50. People say 'it all evens out' but I dont think I always managed to shut down just before it recorded another 0.1!
Seems strange to me that while we plan flight to the nearest minute, most of us record flight tiime in our log books to the nearest 6?!