How do I add departments to the Sharp ER-A420 electionic cash register?

This machine is quite configurable, so it can have lots of departments. It probably hasn't got more than 10 allocated in memory, so it will most likely need more opened in the service area.
The first thing to do is to try programming dept 11. If you get an error then it will need more depts opened. This requires a service key which I can help you with, and it would be best to have the service programming manual when working in this area as it has the extra dealer area information. Check out the preview of it here to see if you have it already:

http://the-checkout-tech.com/manuals/cashregisters/Sharp_ER-A410_and_ER-A420_programming_manual.html

Registerman
July 2010