Faulty instruments - share your stories

[Fallingwater]

I've just spent an evening taking careful measurements of voltage and current draw for two flashlights I'm reviewing, then calculating emitter power, converter efficiency and battery life.

Then I read somewhere that one of the flashlights I was reviewing, and on which I had measured a 300ma draw, actually draws more.

I got suspicious, tried using another multimeter, and the values were higher.

A quick test with the ammeter in my lab power supply shows the multimeter I was using adds way too much resistance and thus has lower readings. Now I have to do it all over again with the other multimeter. An evening wasted

And to think this multimeter cost me more and was supposed to be better... :shakehead

This gave me the idea of sharing such stories here, since there's always something to learn from other people's mistakes.
So, did you ever have frustrating experiences with your instruments?

 

[scott.cr]

Not really electrical test gear, but every single tire pressure gauge I've purchased lately has been off of the other gauges by around 3 psi. So... my tires may be within spec for pressure or they may not be. Could be overinflated, underinflated or ???

Also, about 10 years ago I rented a Nissan Altima for a business trip. The speedo needle would ALWAYS go to the peg. As long as the vehicle was moving, the needle would continue to go clockwise. When I returned the car to the rental agency, the guy that took it in seemed surprised that I put 8,400 miles on it in a single weekend.