Last trip out, my tach was off around 500 rpms at mid range, and around 1,000 to high at wot. Been acting up the last outing too.
It's a Faria gauge, & only thing on back of it is the 6 position pole setting. it is on #5.
I've read where you just turn that dial to each setting & then back to where it was to recalibrate it. Does it have to be plugged in to do this, or can I unplug it/pull it, and do this?

It zeros out when turned off, and idles at around 700 rpms, which is fine.

Thanks,
Jeff