Book contract question

[Reza B'Far]

Everyone on the list:

I've got an offer to author a book and, frankly, I know very little about
what's fair and what's unfair... I've never written a book, just some
articles, IEEE stuff, etc.  Here are the terms of the contract.  Can you
guys tell me what you think?

--13% royalties (based on global net receipts)
--an advance of $5000, 50% paid upon acceptance of manuscript, 50% upon
publication
--publisher will pay for your index

The book is about 900 pages and is on a software engineering topic.

Thanks in advance.

Reza