The new Bel 935 that I used for two weeks that was working flawlessly, yesterday flashed, "CAL????" on the display. I gave it to a friend after thinking the unit was good. Tested it in the big truck for two weeks, let if rest in A/C for a while, took it back out for one day to test, still worked great. Gave it to my friend yesterday then he called me and told me CAL???? came up on the display. This was not a used unit either, I bought it new. I got it back from him and let him borrow my Bel 995 for a while. Man this sucks guys, I have to call Bel yet again.