When I first got my EX1 I assumed that when reading the histogram, far left is black, and far right is white. I thought that if the video level touches the right edge of the histogram box, I'm at 100%. Wrong! Notice that when you close the iris, the indicator doesn't touch the left edge. There is a small gap. Likewise, 100% level is equidistant on the right side. Turning on the multi colorbars and observing your levels will confirm this. If your level touches the right edge, you're at 108%. Don't make my mistake of thinking that touching the right edge is 100%.

I've been wondering why Sony didn't implement in the EX1' s histogram the nice little aid as present on the V1: when you have zebra set to say 100%, there is an additional threshold (brown vertical line) before the RH end of the histogram, at exactly 100%. It is a sort of redundat check, but helps a lot...

Warren,
there's technically no reason not to go to 108%. Of course anything there is clipped, with a capital "C".

The big trap with histograms is they don't show clearly how clipped you are. The trick seems to me to be to start off underexposed and wind the exposure up while watching the readout. Then you'll see how much of the frame is moving into that vertical line on the RH side as it's being clipped. You need to look at that in conjunction with the image to judge how much and what you can tolerate being clipped.