Anything and everything Spitfire.

Hi, IÂ’m very new to the Spitfire world having only bought my MkIII a week ago, but I have a question regarding the rev counter (hopefully not a silly one).
The rev counter in the car can’t seem to make its mind up and swings over a 1500 to 2000 RPM range when the engine is running – so I’ve currently no idea if it telling me I’m doing 3500 RPM or more like 4500RPM etc. Anyway as this is the cable driven type (of which I have zero experience) my question is, is this normal for this type of rev counter or should it be more accurate (I’m assuming yes). With the follow-up question being, if it should be more accurate than this what is the likely cause, gauge, cable, distributor drive gear or anything else ?

Thanks

Mark