KZ440 tacho - how accurate is it

Anyone know how accurate the tachometers are on the KZ440s? My KZ440 is fully sorted (except it needs properly rated 10A and 20A fuses), and I'm just back from a ride. It was a ride to sort of test everything.
What I noticed was that the mech tacho was dancing around. Not badly, but you could tell it was missing a beat at times. This is probably because of the gear inside the rockers cover skipping. What I would like to do is familiarise myself with the sound (engine tone) and vibration of the bike as it redlines, so that I can eventually ditch the tacho and cap off the lead going into the engine. So I went for it. The sound was telling me the engine was maxing out, but the tacho showed 2/3rd to 3/4 full. That's what I felt the redline ought to be. It doesn't skip around a lot compared with KZ440s I've seen on Youtube - just a little. Any thoughts on this?

They are not perfectly accurate, but if everything is working as designed, it should not be off nearly so much as you describe. The best answer will be had by connecting a known accurate electronic tachometer and comparing the two readings.
The dancing around you describe can be caused by several things, but the gear skipping is quite rare. If all the teeth are present and not badly worn down, it is likely fine. It is much more likely that the cable has not been properly serviced and is gummed up or fraying or both. It could also be a problem inside the meter with dried up lubricant, wear, the intrusion of dirt, or rough handling.

Sometimes lubricant fixes a glitchy meter. remove the meter & add a small amount where the cable connects.
As for whether or not the engine is maxing out, you could compare your numbers to the numbers at GearingCommander.  A couple of 440 are on the list of KZs.

Maybe it's the fact that the engine makes such a huge racket, that's throwing me off. Standard exhaust, but the harmonic balancer system probably isn't as fresh and tight as when it came out of the factory. I haven't ridden a twin for a long time. I had a look at that Gearing Commander site - very useful. Will try again tomorrow and compare notes against it.

This could be a possibility. Your tachometer's internal magnet clearance may be off.

Very interesting, cheers.

The bike pulls very well through the gears up to 70mph. It has a surprising amount of pull up to that speed, if you just change gears by ear. More than capable of keeping up with modern traffic, up to that speed, even uphill, and gear selection doesn't seem to matter that much.

Going by the Gearing Commander site, it should reach 35mph-ish in 1st before redlining. It does do that. However, I don't have much faith in my tacho. I don't think I'll be changing up at redline anyway, as the noise is too irritating at those engine revs, compared with 4-cylinder bikes. I think I'll just bin it and be done. Won't even bother with a tacho at all. Thanks again