Magic items with charges and multiple options

[The Sinister Chris]

I'm usually decent at figuring out the pricing formula for magic items, including the ones not listed. However, I've been having trouble figuring out what the formula would be for charges per day if you had multiple options to use the charges on.

For example: a mask that has three uses per day of either see invisibility or blindness (per blindness/deafness) that you can choose how many of the three charges are used on each of the two spells.

This also comes with the question of whether there would be a price reduction for only being able to do blindness, but not deafness?

I'd like to know if there's an actual formula for calculating this that I might have missed.

Thank you in advance to anyone with answers.

[Dasrak]

There are no rules for this sort of thing; the pricing modification that would be incurred in these situations is entirely up to GM discretion.

[The Sinister Chris]

Huh. Well there must be a way to come up with a rough estimate. I know there are items that do this, but the only one coming to mind is Restorative Ointment from the core book (page 526). The problem is I'm drawing a blank (thanks sleep deprivation!).