I also try not to be building factories everywhere simultaneously, as this can leave you vulnerable to a sudden attack, and without a pipeline of freights dropping in every turn.

Barbarossa's math sounds correct. The factory bumps up your shield production by 50%. Assuming that before the factory, your city is pulling in roughly 1 shield per worked square...

return = cost
#turns[benefit/turn] = 200 shields
t [50%(prefactory production in shields)] = 200 shields
t [.5 (population shields)] = 200 shields
t [.5 (p)] = 200
t = 400/p

For a size 10 city that's roughly 40 turns.
(Of course you can tweak the formula to include the fact that the city square itself is worked (400/(p+1)) and the fact that you lose 4 coins (about 2 shields worth? (400/(p+1-2))?) through upkeep but the formula remains roughly the same.)

It'll take roughly
400/(number of shields the city is currently producing) turns
for the factory to "pay off."

However, this indicates to me that the sooner you buy a factory, the sooner it pays for itself (as long as it's not later than 1960 or so). (I'd still be very leery of building one at any time in a city with less than 5 shield production.)

Sure, this calculation makes perfect sense, but this game is full of the unexpected and immeasurable. OK, so it takes 40 turns to "pay off" a factory. What about the immediate benefits that one receives before the factory is "paid off"? Some of these benefits include: 1) the ability to support more troops in a non-fundy government, 2) better use of Capitalism, 3) ability to move workers to food and trade specials/terrain while maintaining or increasing production. The first cannot really be measured and the others actually assist in paying for the factory.

1. At 600 shields, the cost of three factories, Hoover is relatively cheap. The Factory + Hoover combination changes the calculation dramatically.

2. If you have a decent trading strategy, by the time you reach Industrialization you should have piles of cash laying around just waiting to build those factories in one turn. There are few things in Civ more fun than putting all those brand spanking new factories to work turning out tanks to smash the pesky Zulus.

3. Of course one needs to consider the opportunity cost of the cash you have laying around. The oppotunity cost might include bribing the Zulu cities, but that is not half as much fun.

quote: Originally posted by Hawkman on 12-26-2000 03:34 PM The only thing worth considering is whether or not you can immediately afford the upkeep on the factories. If you're worried about payback, then crank out a few trade units on each factory and send them to a distant city. That will keep your cash flow looking good. Buying all the factories in one turn can turn your budget from a nice surplus to a nasty deficit, but the trade units will fix that.

Add to that the upkeep of all those mass transits and/or recycling centers...

Pollution can be easily managed with Engineers.

Factories give you the edge that quickly defeats a player without them.

All the formulas about return on investment are bogus unless they target the true return that factories produce, more units, more infrastructure. That's what this game is about.