This is probably one of the few times where just one d10 is used. In this instance it is a characteristic test using either WP or POW. In this particular instance, the attacker would need to roll lower (lower im assuming that this is showing control than just raw ability) than a 16 on their 1d10+POW/WP. The 16 comes from the difficulty the spell has set in place Intermediate difficulty being 16.
Level: 24 Action: Passive
Effect: Creates a barrier that absorbs and converts to nothingness.
In addition to a conventional shield, any supernatural power will stop
automatically, canceled if the attacker fails to overcome a WP or POW control test against the difficulty determined by the level of the spell(1d10 + WP or POW).
That is, if an opponent launches a offensive power against a magician who is protected behind a Void Shield at intermediate grade, and the caster obtains a successful defense, the attacker must overcome a WP or POW control check of 16 or attack will be canceled without
even damaging the shield. Similarly, any physical object stopped by the shield must pass a PhR test or be destroyed immediately.
Zeon Base(50), Intermediate(90), Advanced(120), Arcane(150)
Int R. Base(6), Intermediate(9), Advanced(12), Arcane(15)
Base: 200 Points of Resistance / Hard 14 / PhR 100.
Intermediate: 300 Points of Resistance / Hard 16 / PhR 120. <--------------------------- difficulty used-----------
Advanced: 400 Points of Resistance / Hard 18 / PhR 140.
Arcane: 500 Points of Resistance / Hard 20 / PhR 160.
Maintenance: 5 / 20 / 25 / 30
Spell Type: Shield
Now I myself cannot find it specifically but Im pretty sure that you add the stat and not the modifier it gives. If the modifier was added then most likely, the attacker would almost always previel easily with just a couple of spells, the shield would be nearly useless to have. Being that stat it would be harder and in my opinion be more defensive as it should be making the shield strong.
If I am wrong someone please correct me. If anything this should be of help and hope i explained well.