Years ago, we were involved in testing a customer's one and only prototype board. (I cannot remember its desired function now). I was not actually included in the testing but thought I'd "help". My work mate was looking for a problem so, even though he had not asked, I had to put my ore in and so, taking up his multi meter, went to measure the 240VAC mains input voltage. But I failed to check the meter and he had last used it to measure on the 10A range! After the flash, when I could see again, there was the board with quite a few tracks blown off the board. Fortunately for me, after a lot of work replacing destroyed traces and parts, I got it going again.