Manufactures are an advanced building which crafts a single item continuously.
You select a recipe (item) to craft and after a start-up time (= 3 production cycles of that item), it will continuously craft that item while you have resources.
Once running, it creates items 40% faster than a Workshop.
That makes that when you need 1 to 7 times a certain item, a workshop will be faster. The manufacture will only outperform the workshop when you let it produce 8 or more times the same recipe before changing the recipe.
