Check Digit Activity (GCSE Computing and other)

Originally created for the new OCR GCSE Specification. This explains how the 10 digit ISBN check digit system works, invites students to modify a spreadsheet to create their own checker and then gives them some real ISBN numbers to check. The unchangeable cells are locked with the password 'password'.
As an extension students could try a TRUE/FALSE game of telling each other correct or incorrect ISBN's they have looked up.