I've been number crunching way too much, but I've to the conclusion that the Vis economy generally portrayed in the books doesn't work. I'll try and explain...
First, some assumptions about the Order and Vis
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The Order is 1000 magi strong.
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Each site (covenant or chapter house) is made up of 5 magi, giving us 200 sites requiring a single Aegis of the Hearth ritual - this assumption is very vague and is based off this being a TTRPG...aka 5 players
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The average Aegis of the Hearth ritual is Lvl30 - again, another vague assumption...
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Therefore, each year, the Order spends 1200vis on Aegis of the Hearth rituals
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Vis produced from sources/finds is evenly distributed between all Arts.
So, those are my assumptions. Now some scenarios.
Moderate Vis
Ref: ArM Core pg 218
10 pawns of vis per magus per year.
This generates 10,000 pawns per year across the Order. Providing, on average 666 pawns of vis per Art
This only just manages to cover the cost of the Orders requirements for its Aegis rituals, if all available Rego and Vim vis are used. But then leaves a surplus of 8,800 vis in other Arts, a truly excessive amount. The stockpiles of other types of Vis become irrelevant. Vim is most certainly the most valuable form of Vis, as without it, magi cannot create any enchanted devices, and it must be generated via Magi performing Vis extraction, a time consuming process.
Low Vis
Ref: ArM Core pg 218
5 pawns of vis per magus per year.
This generates 5,000 pawns per year across the Order. Providing, on average 333 pawns of vis per Art
This fails to cover the cost of the Orders requirements for its Aegis rituals. Then leaves a surplus of 3,800 vis in other Arts, still a truly excessive amount and we still suffer the same issues as the previous paragraph.
My own rate
10 pawns of vis per site per year
This generates 2,000 pawns per year across the Order. Providing on average 130vis per Art.
This completely fails to cover the cost of the Aegis rituals. But it then only leaves a surplus of 800 vis, something far more manageable (but still alot). I get this yearly rate by having vis sources as wealth boons, at 1/10th of their equivalent silver value.
Conclusion???
Without utilising the High vis suggestion on page 218 of core, the Order's vis economy doesn't really function in regards to what types of vis are available for the basic functions of the Order. And even using the Low vis suggestion, the amount of vis within the Order overall is excessive and largely useless. Changing vis source assumptions to be based upon per covenant, instead of per magus, allows the total vis in the order to be more sensible, but then completely cripples its ability to perform basic functions (Aegis, enchantments)...
At my own table, I manage this by making vis universal instead of divided by Art. It nukes hermetic alchemy into the floor and changes the role of House Mercere somewhat, but I find the overall effect more immersive, and less hassle to track various types of vis.
Anyway, those are some random Sunday morning thoughts, interested if others have considered the wider Order's vis economy and what conclusions they came to
Kal