Quite often, ammeters are highly dubious anyway, depending on what you've got. I don't reckon it's anal at all to have the only important instrument working right and clearly!
Lots of cheap ammeters flicker for lack of damping on the needle, some of them the needles tend to touch the face after a few vibes and stop operating smoothly, some of them the terminals become loose on the back and they just fall apart.
If you're really going to buy one, suggest you spend the extra it takes to get a good one. My favourites are the larger Miller ones with white faces and well-spaced -8 0 +8 scales which I can read without my blasted specs on (they also come in black, like Fords did), but they won't fit a BSA headlamp without butchery. Original Lucas ones are fine, with damped needles and a choice of scales (unless you want to have whatever scale the thing's supposed to have had as original).
I think there are other threads here on this, but you definitely get what you pay for.
And of course, per MG's comment, with 12v systems there are only half the amps floating around for any given load so a typical -12-6 0 +6+12 scale and wobbly needle isn't always helpful. But whichever voltage, with a decent regulator and charged battery, you shouldn't be seeing charge rates of more than an amp or two except just after sitting at tickover with heavy loads on. More is not Better - lots of amps says either the battery is weak or that, owing to poor regulation, the dynamo's field coil is being over-served, the armature unnecessarily loaded and the battery over-charged. Badly-set regulators have given dynamos a bad name for half a century.
