Hidden Sheets

Hi

Just a note to say that I love reading this forum and I am beginning to learn the power of Excel!

I have a 15 sheet spreadsheet that has many formula and results that are obtained from a "Master Sheet."

I want to hide the "Master Sheet" from users view.

When I do so the formulae can't find the info they require. How do I hide a sheet so that users can't see it, but the formula from other sheets can still access it?

Regards

Alex