Send him a PDF file of the sheet he needs to see.

Jeremy wrote:
I have prepared a pretty advanced spreadsheet to give to a potential
customer. Because this customer does not have an exclusive agreement with my
company, I would like to build in some security so they cannot see the
calculations and base values.

I tried to hide the sheet with the calculations and protect it. On of our
sales guys was able to break this open in less than 20 minutes.

How can I better secure this?