Hi, my Citroën AX I have fit a tachometer because I am deaf, my tachometer it looks inaccuracy it needs adjustment, my multimeter put the four cylinders on and connect to the W+ on my alternator, one on the chassis, my multimeter shows idle is 624rpm but my Hayne said 895rpm, and it won't show over 1,999 rpm it comes out like this ---- It makes me wonder the multimeter is not accuracy.

If I buy a laser tachometer to point to the cam belt, would this work accuracy rpm?

thanks