Depreciation is a Financial Accounting term used to describe the estimated useful life of something in terms of resources (money in real life). There are three methods, factories use the “units of production” method rather than either of the other two. The idea is that we can only expect the factory to produce so many of a unit before it is lost, and anything after that is an altruistic bonus from our opponent(s). Since we will never know how many unit will actually be produced from a factory before the game ends or the factory dies; we have to establish rational goals instead. As an example, every nine seige bots produced justifies constructing one new factory and upgrading it to tech 3.
Here is an example why…
Each seige bot costs about 1/9 of a T3 factory (including upgrades); therefore each factory must produce at least 9 seige bots for the total cost of those 9 bots to be 1/2 fixed and 1/2 variable costs. If we can expect to need 50 seige bots to overrun and destroy our opponents, then we will obviously need more than 1 factory to produce them. We also know that building 50 factories is a waste of both time and resources. The fastest way to produce them is to have factories numbering (SQRT of 50 = 7), but that may not be economically beneficial. In this situation, 5 factories would be economically superior to 7 factories (without sacrificing too much time).
If we could expect to need 500 seige bots, then we would want to have at most (500/9 = 55) factories and at least (SQRT 500 = 22) factories. With 22 factories we would produce at the fastest rate with the lowest total cost (fixed + variable).
Factories needed = seige bots / 9 … or… SQRT( total seige bots ) [whichever number is lower]
To make this scenario more realistic, we will add one more layer of complexity (and we’ll assume that those 500 siege bots will be used over the entire game instead of all in one attack). All T1 Factories have a build rate of 10, T2 of 20, and T3 of 30 (double in FA). All engineers follow a similar progression of T1=5, t2=10, and T3=15 (we’ll ignore support commanders because they’re not supposed to be used primarilly for construction) (same build rates for FA).
Six T1 engineers will effectively count for an additional factory. However, six T1 engineers cost 6/98 as much as a new factory and 6/58 as much time. Putting more tech 1 engineers around the same factory increases production linearly.
The only limitation to having an infinite number of engineers assisting the same factory is the time it takes for the unit to leave the factory. Through experience, up to 16 engineers may assist a land factory without significantly blocking the path of the unit leaving (minimizing downtime). Air units fly, so this limitation is effectively non-existant (use as many engineers to assist an air factory as possible).
The cost of engineers is insignificant compaired to a T3 factory, so we’ll ignore it. The relationship of time to build engineers’ at different tech levels is:
T1 = 150 T2 = 440 and T3 = 980 (for Vanilla, the spread is even more dramatic for FA)
Assuming we’re still building seige bots and not spamming lower tech level units (a valid strategy)… the maximum number of factories would have a simultaneous build rate of 1650 and the least we could accept has a build rate of 660. Using 16 T1 engineers gives us a combined build rate of 120 (80 + 30 from the factory). We need a minimum of 6 factories with this set up. If we use T3 engineers, 16 gives a combined build rate of 270 (240 + 30 from the factory). We need a minimum of 3 factories with that set up. The maximums are affected by the fact we’re using engineers instead of upgraded factories. Tech 1 engineers assisting a factory require it to construct 11 seige bots to depreciate fixed costs. Tech 3 engineers require 24 seige bots to depreciate fixed costs. While the (fixed + variable) cost of each siege bot increases by +22% and +166% (respectively); the production speed of each one produced increases by +300% and +800% (respectively). We could use up to 45 factories with T1 engineers or we could use up to 20 factories with T3 engineers.
The least amount of time and resources will still use (SQRT 500=22) factories, but with Tech 1 engineers assisting it will take 1/4 the original time. With Tech 3 engineers, we would not produce enough seige bots to fully depreciate our fixed cost, and so we want to use the lower number of 20; which will take about 1/9 the time to complete production.
