I've noticed that when I go to change a weapon, the one that I already have equipped has a green 'plus' amount next to it.

I obviously know that the red 'minus' & green 'plus' next to other weapons/apparel mean that they're stronger or weaker than those you already have euipped but what does this number denote when you already have the same weapon equipped as the plus number is next to?

This has perplexed me for a while. I'm sure it's something really simple but it evades me completely.

Any help would be appreciated.

Anybody?