Found it (Y279) thanks for all the help.
If you are willing to lock the item down to
only ever being useful for one specific spell—
such as an established evocation rote or a divination
spell that always looks for the same
thing—then you get a single free “slot upgrade”
(as described below) to add an extra +1 bonus.
You can’t benefit from the same type of bonus
(e.g., a control bonus) from two or more items
at the same time—so if you had two items, one
with a +2 control bonus and another with a +1
control bonus, the total effect is a +2 to control.
Example: Evan Montrose has three focus
item slots. He could make a single wand that
takes up all three slots, giving him +3 offensive
power for wind evocation only, or he could split
the bonuses up, for +2 offensive power and
+1 offensive control. He could also make it
more multi-purpose, taking just a +1 offensive
power bonus, but applying it to wind, water,
and earth evocations.