How does Treasury in Heroes IV work?

There is a Treasury building in the Academy castle in Heroes IV, which gives "additional 10% gold per week". 10% of which gold? Total gold in my budget? Gold brought by village/town/city hall? When does it occur?

Is this structure worth building?

It adds 10% to your current gold per week. In Heroes 3, you'd simply get a 10% bonus to your current gold at the start of a week.

As Heroes 4 changed everything to work daily instead of weekly, you now get a 1.43% bonus to your current gold each day. You can click on the treasury to check how much it produced yesterday.

It is generally a very powerful building and rewards you for holding on to your gold a long time.