Dancing RPM needle

[headlights]

Dancing RPM needle. Just put car back on road after 4weeks, changed ignition leads and plug extensions, rpm needle now dances around actual rpm +/- 400 rpm, and looks like it under-reads some of the time. Is this just coincidence? Engine running perfectly. Any ideas ??

[headlights]

Thanks for all the replies. The Rev counter is in the post to Peninsula, They recon the problem is circuit board in the rev counter. Should get it back end of next week. Watch this space!. Has anyone changed the clock for a volt meter? thought I might do it while the dash in in bits.