While looking at your web page it occurred to me that I owe the company my appreciation for avoiding a disaster in my 421C.
Some years ago I put dual JPI slimline tach and MP gauges at the bottom of my panel. Though I have had some issues getting them to operate consistently, I have always used them as a check against my principal flight instruments.
The 421 was based for years at San Carlos (KSQL), an airport too short for a balanced field takeoff, even on cool days.
On a takeoff run, just before rotation, one of my mechanical tachs died; a nasty event even in flight. One glance at the JPI tach for that engine convinced me that nothing other than gauge failure had occurred and I simply kept going. The alternative would have been cut power and brakes, which would have put me through the chain link fence at the end of the runway.
As a backup, your instruments saved me a very large repair bill, and perhaps the airplane.
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