I had this idea for a podcast article, but wanted to bounce it around here first.
Gang, if we allow negative numbers, I think it makes the magic system easier to use. I want to run this past some other sets of eyes because when I did City and Gild, the playtesters vetoed percentages, then 5%/10%/20% as too difficult, so maybe I like numbers more than other people. On the off chance: here's what I'm thinking. By using negative numbers we can take out the change of scope in magnitudes. You know how it now goes Base 1,2,3,4,5,10,15... and the adjustments are +1 Magnitude for each change of Range above Personal, Target above Self, Duration above Momentary, and volume?
What happens if we instead make it Base -15, -10, -5, 0, 5, 10, 15...and the adjustments are +5 for Each range above Range above Personal, Target above Self, Duration above Momentary, and volume above (in this case) an Animal of Size 0 or less?
So far as I can see, for spells with a Base Effect level of 5 or more, there is literally no change.
For spells with a base effect of less than 5, the math is easier because it is in clear steps.
If the ultimate level is less than 1, it would have been so close to 1 in the old system as makes no odds. So for magic item creation you'd deem it a 5.
Flattening this way doesn't seem to affect the Arts progression.
It may make it easier to rework magnitudes, which might draw the Ability and Art frameworks back together in some variants.
Flattening this way, if it works, may open the way to changing what counts as 0, For example at the moment the system is designed around Forumlae with sponts as Casting total/2 or 5. You might instead design it around sponts, with no fatigue halved and formulic doubled.