Hi Jimi D. It is an Excel spreadsheet, so it will need some software in order to edit the values. It does not have to be Excel though. I have just tested scuba's calculator on the completely free Open Office software (v3.2) and it appears to work fine, including the macros. You can download OO here -
OpenOffice.org Downloads . Another free spreadsheet program I'm aware of is Google Docs which is a web app which is mainly compatible with Excel files. However I've not tested the spreadsheet on that.
Hope this helps