I've been wondering something about the use of plus lenses. Can you "stack" 2 lenses together in order to produce a more powerful lens? For example, say you have a +1 and a +2 lens, and you want to have a +3 lens. Can you put the two lenses together and end up with +3 diopters of correction when you look through them? Or does it not work that way? Anyone experimented with this? I'd like to avoid buying any more reading glasses and just make use of the ones I have as my eyes progress.