I'm looking at the example spells in Thaumatology: Ritual Path Magic and the very first example, Air Jet, seems to have an error in the calculation of casting cost.
I'm aware that SJG sources often use what seems to me a bizarre method of calculating costs; if they add or subtract a percentage, it's a percentage of the original cost, not of the calculated cost up to that point (IOW, 10 - 20% - 40% would be 4, not 4.8 rounded to 5).
Here, we have Greater Control Matter (5), with modifier Damage, External Crushing 3d (+8, though this isn't written in the spell block -- itself with Double Knockback +20%, Jet +0%, No Wounding -50%).
Based on TRPM 39 and Spell Modifiers on TPRM 18, then, I see 5 + 8 (= 13) + 20% (of 13, = 15.6) - 50% (of 13, = 6.5, so total of 15.6 - 6.5 = 9.1 rounds to 10), so x3 for one Greater effect ought to be 30. Am I misunderstanding the calculation method (very possible), or is this just a calculation error that got past the editors?
On further reading, I now see that External Damage is tripled for a given energy cost, but now the error runs the other way -- 1d (which gets tripled to produce the External Crushing 3d) is +0 which is still zero after applying +20% and -50%, so either this is (5 + (0 +20%, -50%) = 5) x 3 = 15, or it's (5 + 0) + 20% - 50% = 3 x 3 = 9.
If it matters, I'm using the PDF v 1-1, purchased and downloaded from Warehouse 23 last night (so it's presumably not an old edition).