Test Gear WM "off" ?

Hi, my Test Gear waveform monitor seems to be a bit off as far as the chart goes. I have a clip which I used levels on to limit it to 16-235. I set the scope's preferences to 16-235. But when I look at the scope, the 16 area seems to be hovering over the zero line by a few pixels, and the whites are also peeping up a few pixels above the line. I double checked and my clip does have areas that reach to 16 and to 235. Any ideas?