There is either a typo in the description or this improvement is not giving what is says it gives.
The description says 25% reduced build time for improvements.
The bonus is 20% increase to mateials produced by this settlement.
btw, how do I put a screen shot in here? I have the picture in say c:\games\bug.jpg but when I try to insert it using insert image and input that path into the link url, it does not load the image.
