Is there a performance difference b/w different brands. I have a cheapo $20 Ratshack model that I can't seem to measure the resistance of something. If I test across an actual resistor, it bobs up and down and then settles pretty close to the mark. With this thing I'm testing now, it bobs and then flat lines. I'm wondring if maybe I'd have better luck with a nicer model or if I'm just unskilled.