So I was reading up on Gruagach for no particular reason (don't laugh, Michael) when I actually read the text of the Flexible Casting spell mastery properly for once.
"The gruagach's Mastery Score is added to the number of levels by which he can vary the Range, Duration, or Target of a known Formulaic spell."
(HMRE p59)
This seems a bit underwhelming. Unless you are talking about very low level spells, it's going to achieve exactly nothing until the gruagach hits Mastery 5. Even with Flawless Magic that's a considerable investment of experience points in a single spell. Should this have been dealing with spell magnitudes? Or is that too much?
Bear in mind that one of the potential integration breakthroughs is to replicate this mastery ability in Hermetic magic. At the moment I'm wondering why anyone would bother.
apparently doesn't talk about spell levels, but levels of Range, Duration, and Target.
So with level 1 of the Mastery, the Gruagach might increase Duration from Momentary to Diameter without changing the spell level.
That is pretty solid - and would be absolutely worth integrating to Hermetic magic. The SG will have to judge the possibilty of increasing an R/D/T to a value which would make the spell a ritual, though.
Ah, I see. That's... remarkably unhelpful. Everywhere else the discussion of varying RDT refers to spell levels, and the variations do change the final spell level. I don't like the idea that this mastery doesn't change the spell level, are you sure that's what's intended?
Either way, it looks like this is a good candidate for an erratum!
It probably does talk about the spell level.
The virtue Flexible Gruagach Magic says
Instead of being
able to vary the Range, Duration, or Target
of a known spell by 10 levels, the gruagach is
able to vary the spells by 15 levels.
The description of Gruagach spells say
Gruagachan are able to vary the effects
of their Formulaic magic to a certain extent.
They may cast any of their known spells
with a different Range, Duration, or Target.
The final spell must be within 10 levels of the
original spell and the new Range, Duration,
character. Casting success, Fatigue loss, and
Penetration are all calculated based on the
casting level of the final spell. This works the
same as the Hermetic Virtue Flexible Formu-
laic Magic, but allows the gruagach to alter
10 levels of spells.
Every use of the word "level" here seems to refer to spell levels
Your second quote is from p.59 Gruagach Spells, describes the flexibility of standard Gruagach spell casting, and uses spell levels throughout.
So Rhodri James' quote from p.59 Spell Mastery "The gruagach's Mastery Score is added to the number of levels by which he can vary the Range, Duration, or Target of a known Formulaic spell." can indeed refer back to that quote - hence also speak of spell levels.
The Mastery Ability read that way "seems a bit underwhelming" indeed - but that's the rules with that very plausible reading.
I am the SG, so that's easy. I'm going to treat the mastery ability like the virtue, and say each level of mastery adds five to the number of levels the gruagach can vary the spell by. Not that it matters, since the only gruagach every likely to show up in my saga is an NPC, but it's the principle of the thing.