General Spell Guideline Rules?

[ExarKun]

it seems you double-posted this here: How do general guidelines work?

My answer there is:

@ExarKun

Generally speaking you choose a base level.
Say 20.
You read the description of the guideline. In the PeVi example it is base +2 magnitudes iirc. You then chose parameteres. Voice, which is +2 magnitudes.
Your spell is level 30, and destroys 30 might points.
So for this example spell, the "destroying" power is equal to the level, because of the parameter.

Should have the parameter of the canon spell been sight, your spell would have said that its destroying power is "level of this spell -5".

For your RoPD example it is this: chose a base. Say 15. This creates a substance doing +20 damage. Now you need parameters, durations, etc.

As for the long term fatigue, no. See RoPD p69, second column end of the first paragraph: "Magi may use this special vis when ceremonially casting spells, but not with other kinds of magic or laboratory work — actual vis must be spent to enchant a magic item or study the Hermetic Arts." Casting the longevity ritual is not a spell because you don't have any casting total.