The group I'm playing with is very new to the game, and our DM also has a million things going on. Last game we ran into an issue where we all didn't have the rules and formulas down as firmly as we should and we spent 20-30minutes fumbling around trying to figure out whether a player even had the ability to try for it. While we use Roll20, it doesn't really have a way (that I know of) to figure out the success threshold for the spontaneous spell you're trying to cast.
So, I went ahead and tried to make a cheat sheet that lists all the important stuff, clipping pieces from the rulebook, and then ultimately adding a calculations tab near the bottom. The calc tab doesn't calculate for fatigue, just what you'd need to roll to successfully cast the spell.
I wanted to share it with all of you but also to see if anyone is willing to review the info and the calc to make sure I didn't miss something or screw up the formula. If it's all accurate and you'd like to use it for your own game, please feel free to make a copy (think I set that permission right!).
Hi! I love using Google Sheets for these things; You should see the mess of a Verditius Lab Total sheet I made. I'll take a look at it later after work and get back to you.(Not going to delve during my coffee break.)
I would suggest using a bit of color coding; I've always found it helpful for use. I like green cells for places to change actively (the spell you're casting right now); Yellow for stable things (The magus arts and abilities); Red for things that the user should not change (formulas and outputs).
While my group uses regular spreadsheets, our sheets are bigger. On it we have a list of the Forms with: Casting Total w/ Technique (TeFo + Stamina), Fatigue Spont Roll, No Fatigue Spont total, Magics of Gestures (no fatigue modified by Quiet Voice & Subtle Gestures) and Magics of Thought (no fatigue modified by No Voice & No Gestures). We also have a modifiers box with things like: Fast Cast (Fatigue), Fast Cast (No Fatigue), Ceremonial (Fatigue), etc. There is even a note for Aura Modifier (/2 Fatigue, /5 No Fatigue).
We got the idea from a Sub Rosa and expanded on it to have every thing calculated out ahead of time. It lets a player know exactly what they can do at a glance.
Anything classified as a "Magic of Thoughts" can be done with no effort, risk, or discernible casting. Things of this level just happen around a Magus, since their understanding of that TeFo combination is sufficient that it is a purely mental exercise. Of course since they have no sound Voice range is worthless for them. Any TeFo combo in which you have a 20+ Casting Total (not counting Aura) will be 1+ here and can be used as long as there is no negative aura modifiers.