First off, there's a setting on the meter itself that lets you choose between probe, light, and something else. Set that at light. You will be pulling the trigger to start the light flashing and you point it at the timing marks on the pointer and the balancer. Then, with the engine at 2000 RPM, you use the buttons on the light (assuming that you have the DTI light) to "move" the line on the balancer. When it is in line with the line on the pointer, you can let the engine go back to an idle and look at the readout on the meter. That will give you your current timing setting. You will use that number and nothing else. If your timing isn't where you want it to be, shut off the engine and rotate the IP to get it where you want the timing to be set at. Simple as that.
I don't think that the high or low trigger points matter with the light. You won't have to worry about that.