Analog vs Digital Gauge Accuracy

[npm108]

I was wondering how come my analog tacho differs quite a lot to my Merc System Monitor.

With the Merc Analog Tacho set at 5,000 the System Monitor shows around 4800. Was surprised to see a good 200rpm diff, sometimes even 250 perhaps.

Is this normal?

[Turbodiesel]

Not sure why they would show a difference but i would go by the system monitor as its taken from the ecu which should be much more accurate.

[9D280]

Is it a constant offeset?

Analog tach should be counting the same pulses as the ECU, if it's a constant offset then your analog gauge is not sitting right relative to it's scale on the panel behind the needle. (Mine has a "cal" adjuster on the back, but not all do)


Note both gauges' readings at idle & 500 RPM intervals up to WOT & post back the results.

[npm108]

Thanks will compare the two at idle etc and see if there is something I can adjust.