what do the numbers mean on welding helmet lenses?

[JohnBuuu]

what do the lens numbers mean on welding helmets?
for instance, i just have a basic speedglass utiliy welding helmet, and the lense is designated a "3/10". What do these numbers stand for?
i need something a little bit lighter than what i have now (i cant see the weld puddle as much as id like to) so im trying to figure out what to get.... i dont want to do any damage to my eyes, but i feel like im compromising my view. what does everyone suggest/use on their helmets...
oh, FYI, miller 175 MIG machine.
thanks
~John
btw, ive lurked around here for some time, but this is my first post, great place you all have here.

[BillC]

Hi John,

My semi-educated guess would be shade 3 off and shade 10 when the arc is struck. From my personal experience shade 10 seems too dark until you learn to read the puddle, then it is too light...

All the self-darkening hoods offer full UV protection regardless of shade. But, if you see a green spot after welding then your lens is too light...

[JohnBuuu]

thank you for the response,
im going to go back and do some practicing and see if i really should go lighter or just learn to work with what i have better.
the problem im having is that, say if im butt welding something, im having trouble following the seam just ahead of the weld, so the weld might veer slightly off where it should be.
maybe putting some good light onto the work would help?
thanks again
~John