New entry from last entry (scripting)

New entry from last entry (scripting)

I am new to Zoho, and I found it is a solution to my database problems, and I think it is really good.
I started setting up my database this evening, and although I managed to get the right fields for most of my questions, there are a couple that I'm not sure what to choose. I think it may involve scripting, and as I'm not sure where to start, I'm seeing if anyone might know the answer.

I started my company (I sell mugs from home) very recently, and up until this evening, I have been using Excel as my database. It was OK, but I really wanted a program that was designed specifically for that purpose. I then found Zoho, and thought it was the complete solution.
Every order with my company is given an order number - we've started at A001, and then it work up to A010 (for the tenth order), A100 (for the hundredth order), then B001 (for the thousandth order). At the moment, in Zoho, I am entering this manually, and I am having to cross-check it with my Excel spreadsheet to make sure I am on the right order number.
What I am trying to do is find a way for Zoho to remember (or find) the last order number, and calculate what the new order number will be. I haven't a clue how to do this, so I'm going to see whether anyone knows.

If you can give me any help on this, it will be gratefully received.