Larry Dighera wrote:

Was that a mechanical tach?

I would write a report of your experience detailing the equipment
failures that occurred, and politely and respectfully send copies to
Cessna and Garmin. If you word it, so that it contains implicit
references to their exposure to civil liability, and express your
disappointment with the performance of their products, who knows how
they may respond. They may try to appease you with a perk or two. If
not, forward the report to AOPA, FSDO, and AvWeb. :-)

And a NASA Report.
--
Gene Seibel
Gene & Sue's Aeroplanes - http://pad39a.com/gene/planes.html
Because we fly, we envy no one.