Originally Posted by
The_Pink_Panther
Whopity - I didn't realise that the tacho only started counting from above a certain engine speed. ?
Not quite what he said. The tacho time actually counts cumulative revolutions. It matches real time at a certain rpm. For example the tacho time might be set to advance by .1 hours every 13800 engine revolutions. If you were running at an average of 2300 rpm, it would take exactly 6 minutes (0.1 hours) to tot up this many rpms and tach time would equal 'real' time. If you were running at 1100 rpm it would take over 12 minutes to add 0.1 tach hours.