This is a fully-fledged explanation, but I think this is an appropriate project for an intermediate spreadsheet class: designing an interactive timesheet.
This project includes:
- Automated dates
- Automated names for the days of the week
- Separate regular from overtime hours and/or any types of hours for which billing is different
- Date and time formatting for input
- Default values
- Totals for days and weeks
- Error traps
- Data Validation
- Worksheet protection
Via Susan Harkins at TechRepublic.