Hogan, this is for the stamping that goes on the pressure vessel nameplate which designates the level of radiography applied to the vessel.

On another note, man, those RT designations can be a bit tricky, especially the RT-3 and RT-4.  RT-2 took me a while to figure out also, but I understand it pretty well now.  In any event, the AI should be able to help understand the application of these designations.

Make sure you take into consideration what joint efficiency you are trying to obtain also, to determine amount to be radiographed.