ECU vs rev counter

[gav]

Hi all
Just had a great day today sprinting thanks to the fuel injection solving all of my earlier reliability problems. The car ran faultlessly all day.
Interestingly (well to me anyway) the Tacho seemed to be lagging the ECU (emerald) - when I flawed the throttle, the gear change light (set at 6,900) came on ahead of the Tacho which was showing 6,500.
The question is which is likely to me most accurate?
I'd be interested in thoughts
Thanks
Gavin

[PeterK]

The Emerald ECU, almost certainly, which I guess I s counting the pulses directly from the crank sensor.
Peter

[AHM]

Accurate and rev counter need not be mentioned in the same sentence as ECU.

There is an adjustment pot in the rev counter so that you can "calibrate" it. There are also several tachometer and strobe apps for your phone (unless that is still attached by a cable to the wall )