Karl Townsend wrote:

I put a http://www.tinytach.com/ on my tractors five years ago. Very
useful. It wore out the battery and i got another. the new one desn't
work because it picks up signals from all spark plugs. I just got off
the phone with their very nice tech. service guy. The old units, model
4C had a filter. The new ones, model 4A, don't. He's finding an old
one to get me going.

OK, that works, this time. But the other tractor will wear out soon
(five year battery life) so i need to get something else. I REALLY
like the digital readout. Anybody suggest a inexpensive tach to
retrofit to an old gasoline engine? I need to know 1350 from 1325 or
1375 RPM.
Can you crack the case open and replace the battery inside?

Jon