I have what seems like a weird problem with a Fluke 88 (I suspect this is pretty similar to the Fluke 87). The display (and sometimes the backlight) will flicker on/off when I rotate the selector knob. In some cases, it'll actually stay on when in the off position. It usually settles down pretty quickly when you take your hand off the knob, but occasionally you have to physically poke at or tweak the knob a bit to get it to actually shut off. Any idea what the cause is or how to correct it?