ReefNet's website (or googling diopter) would fill you in better than I could but basically the diopter is telling you the optical power of a lens. Store bought reading glasses run from +1 to +3 diopters typically, the +3 being the stronger or the one that will make the print look bigger.
The + 5 SubSee is half the power (strength) of the +10. I use a G10 that zooms out to an equivalent focal length of 140mm. If I use the +5 lens I can multiply the image size by 1.8 times and if I use the +10 about 2.7x (ReefNet's calculations).
Doesn't sound like much, right? Say you are shooting a blennie though that's oh, 7mm in diameter. W/ the +5 the blennie would appear about 12.6 mm across (on the screen or sensor of your camera). W/ the+10 about 18+mm. The term "super macro" is typically appled to these sorts of magnifying powers and they are a practical, upper range for most photogs not doing highly specialized close-up work.
Remember though, photography is a series of compromises. These magnifications make it harder to focus accurately, offer very limited depth of field and any movement (the camera, you, the subject etc.) becomes extermely problematic for sharpness. Still, if you want to get large, highly detailed shots of real tiny things it's a cool system. // ww
