My character has a large mirror hanging in her laboratory. Invested device, silver, large, 6*4 = 24 vis to open.
It seemed obvious to throw an item version of Eternal Repetition in a Bottomless Pool (Cov 101) into it. +1 level for an additional use per day, in case I want to work late into the night, and we're fine, right? Except that as a Lvl 35 effect, this D:sun spell causes warping to my target book every day that I use it to study a summa. So instead of letting me study from an ancient texts while they're safely stored somewhere else, this spell is actually damaging my book!
Okay, so what if I make the "accept commands" a separate part of the mirror? This would be doubly useful, since I'm cough cough absolutely NOT planning to enchant a bunch of other scrying spells in there later.
"Comprehend the Hidden Command", MRB 99
InMe Base 15: Read Surface Thought, +1 Touch +1 Conc +5L item maintains = InMe 30
And now my version of Eternal Repetition drops 2 magnitudes for "accept commands", and goes from D:Sun to D:Conc/item maintains, and +3L for Linked Trigger. CrIg 28 -- just barely under the threshhold for causing warping.
But what happened to that extra use/day? As a Dur:Sun spell, I needed at least 1 extra use/day to be able to use it all day and night. The description of Concentration effects in MRB 99 says that "item maintains concentration" effects will fade at sunrise/sunset "unless the user maintains concentration," so do I still need an extra use per day? Or can I just require the user to concentrate on retaining the spell at sunset?
If I need the +1level, then doesn't "Comprehend the Hidden Command" need an extra level too? Except that it is book published and there is no errata for it.
Tangent: Instead of Touch, can I use Eye to mean that you have to be looking directly into the mirror to give it a command? That would make it easy to booby-trap later with some "Detect Enemy/Cast Offensive Spell" magic that was also R:Eye.
Also, the "Assassin's Bell" (HProj pg 82) gives an interesting twist. It enchants the bell to actually give it a sense of hearing. Can I use InIm in a similar fashion to allow my mirror to accept verbal commands by giving it a sense of hearing? How would that work?
+2 D:Sun, +3 T: Hearing +4L for constant effect, but what's my base? Base 1, for using 1 sense at a distance?