The point to this thread is to discuss and centrally locate my thoughts on magic items which are likely to be common to multiple covenants and their impact on those covenants:
Abluere Magica- this device essentially takes a days worth of laundry and reduces the task to one hour's worth of work. The largest impact is that it will not require ingredients used for cleaning such as lye, and thus should reduce consumables in a manner of a soap maker- however unlike a typical soap maker this is the only produce that it saves (as opposed to other byproducts, which likely vary) and it only saves soap for use on clothes, not individuals. Thus maximum savings in consumables will be equal to 5% of total expenses for consumables. There is a maximum absolute value on this, but it would be the equivalent to a servant using the device 10 hours a day year round- the equivalent of 10 full time washerwomen. assuming that laundry normally requires 1 washerwoman's day of washing per month for every 10 points of inhabitants, this would be an upper absolute limit on consumables savings of 48 mythic pounds per year. The actual labor savings is as defined- for every 10 points of inhabitants (2 servants) it reduces 1 days work per month to a single hour's work. Assuming 80 days work at 10 hours per day per season per servant, 2 seasons per year, a single servant abstracts to 160 days work per year, and the device saves 9/10 of a day 12x per year for every 10 points of inhabitants, or 10.8 days for every 10 points of inhabitants, or equivalent to one servant for every 148 points of inhabitants, to a maximum of 20 1/4 servants at 3000 points of inhabitants. Fractional servants should be tracked until a total is reached and then number of servants required should be rounded up.
The Dumb Waiter- while this device certainly makes service of food far easier and more efficient, it only replaces a set of servants for a short period of time each day- essentially the 1 hour of lunch and 1 hour of dinner. while the upper limit of the number of servants it can replace in this manner is vast, the actual number replaced is limited by what the expected number of servants that would be assigned to this task would be, what they would do with the remaining 4/5 of their day and what use they make of their saved time. if a typical dining situation is assumed where a single server would handle 40 points worth of inhabitants during a meal (4 magi in a summer covenant, 20 craftsmen in a spring covenant) and the reassignment of hours is assumed to be optimal (assisting with tasks within the kitchen or cleaning) during this time, this item would save 1 servant for every 200 points of inhabitants, with fractional servants counting as above- maximum servants saved is not worth calculating since the covenant size to require those savings is beyond the reasonable scope of the game.
This device will however allow a magus to utilize the overtime laboratory routines with a one step reduction in penalties (overtime has no penalties, double overtime is penalized as per overtime, etc) provided their lab is within 500 paces of the kitchen and the kitchen has a arcane connection to the lab. Given that the typical aegis is 100 paces in diameter, this should not be a difficult arrangement in most covenants.
Sight of the Wounded Prey: based on the 11th century fish trap found in Poland, a typical trap holds 4000 fish of medium size, at 18 pounds per fish, means 36 tons of fish per haul. The number of hauls will vary, and the enchantment certainly speeds this, but it can be assumed more expensive fish will also be more scarce. Based on low end fish from city and guild (50MP per ton) and assuming that the bait will entice one fish to enter the trap every three seconds the trap will fill in 20 minutes, allowing 40 minutes to be lowered into and removed from the water it will produce 36 tons of fish or 1800 MP worth of fish per haul, though it can be assumed only 50% of this has actual value after cleaning, with the cost of the crew to operate the trap being assumed as part of the value loss as well, meaning a typical 10 hour day provides bulk fish valued at 9000 MP. As per limits for specialists in covenants this may only cover 20% of covenant provisions costs if used for cost savings- as a source of income this is limited by market conditions and the ability of the available market to absorb this kind of production before prices fall drastically. Assuming it is used 2 seasons per year by one crew at 80 days per season this will produce a maximum income of 1,440,000 mythic pounds per year per trap so enchanted, though it will be extremely unusual market conditions that would allow such revenue to be realized.
Assuming that market conditions are more of a limitation than productivity, these traps still give a +5 bonus to income variation rolls, as well as covering 20% of provisions based expenses.
The motivated plow: This item will plow 1 acre of land per day with 1 grog working it, the same work as was traditionally done by 1 ma and 1 ox. Assuming this would be the typical usage of the ox this device essentially saves the upkeep for 1 ox.
Pipes of eternal bounty: provides a +3 bonus to income variation rolls for 1 agricultural source of income.
Mead for a Day’s Revelry- converting water to wine (mead) still provides nutritionally with a duration moon similar to brewing- as such this device will reduce costs of provisions by 20% up to a maximum savings of 1825 MP per year.