Magic Staff charges

[Penn]

The wording on investing a Staff includes this line:
"When invested during preparation (but not if invested at other times), the staff gains a number of charges equal to your highest-level spell slot, though it can never exceed its maximum charges."

How many charges does this mean? When I make a 7th level Sorcerer (3 4th level spells per day) is that 3 (number of spells) or 4 (level of spells)? Is it something else? I know there's also a cap per staff, but I'm trying to figure out what the words here mean.

Thanks.

Penn

[Thaliak]

It's referring to the highest spell level you can cast, meaning that a 7th-level sorcerer would add 4 charges to the staff. The "number of spells interpretation" is understandable, but it would create a situation where sorcerers would rotate between adding 3 and 4 charges rather than gradually getting better.