I found out my T's diopter measured 13 so I think that makes it a -1.5. It works well with my new progressive prescription. I can put my eye right up to it, can see a lot of the screen, and works looking thru the middle of my lens. On the E it measured 12 so -1.5. I can use it but I have to look through the reading portion of my glasses which is more awkward. I think I'll try and find a -0.5 for it. If anyone wants to trade, let me know.