Awe shucks Bob - that's just too easy
I just looked in my ancient parts box and there it was !
a genuine Fowler Vibra Tak
reads from 2000 to 15000 rpm.
I now use a 'lectric thingy " which I don't accidently stick in the prop --
also I am still hung up on 35% oil - but the only adverse effect is that my engines read rpms too high --
somthin wrong here --