Yep, agree with Rik, the Eye One is better, and should be fine calibrating a plasma.
Bear in mind also that changes in temperature (particularly during a calibration session) can affect the accuracy of meters. So if you plan to have the meter resting on the screen to take measurements (and plasma's can tend to get quite hot) have the screen running for half an hour or so with the meter resting on it, so both are at 'operating temperature' before you start calibrating.
Alternatively have the Eye One on a tripod a few inches from the screen, though if your screen is anything like my friends Pioneer (which doubles as an electric fire - though one with a very good picture), temperature changes may still be someting to factor in.