Tacho reading different to ECU Talk reading

[Wetty]

Hi All.
I did a quick search but couldn't find anything about my issue. My tacho reads different to my ECU Talk gauge by about 150rpm across the entire rev range except at idle where it's spot on. . . . I am guessing the tacho reading can be calibrated by Nissan somehow, but I am surprised at the difference given the signal comes from the same place. the needle sits at zero when the car is off, but as the revs increase the tacho reads higher so at 100kp/h the tacho is showing 2700 RPM but the ECU Talk module is reading 2550 RPM. I was wondering if anyone else has the same issue or can explain it?
Cheers
Andrew

[GeeYou8]

The tacho is only really there to give a rough indication of rpm, idle is quite important so they make it right there, there is a stop that makes the pointer read zero when there is no input. I have not checked OBD2 output vs indication but now I will have to.
Is there any reason you need accurate RPM indication?
Graham

[Wetty]

Is there any reason you need accurate RPM indication?
Graham
Not really Graham, just curious is all. . . . . I have been fiddling with the old girl lately and it was just one of those things I'd been wondering about :D

[jff45]

With modern electronics they should both read the same especially as they are both getting their signal from the ECU.
The gauge would be the most likely to be incorrect, probably something on its circuit board. It's only basically a voltmeter after all.
You can buy a cheap digital laser tacho - $20 Ebay - to compare. They're surprisingly accurate, I found.
Other option is connect a USB cable to the Ecutalk and run a different software like OBD Scantech to see what it displays.

[GeeYou8]

I would put money on the analogue indicator being less accurate than the digital. It is cheap to build an accurate digital indicator, not cheap for analogue.
This is why speedos are allowed up to 10% error, initial tacho error was around 5%.
Graham