I have selected a **5 column by 20 row block** in an **Excel 2003 SP3** spreadsheet. I have selected **Sum** from the quick calc options in the **status bar**. However, the status bar shows a total of £24,000 when it should be ~12,000. **The Sum calculation is wrong.**

I have done the following to try and diagnose the cause:

- Reviewed each cell in the selection for a value hidden by colour formatting (none).
- Tried to Unhide any potentially hidden rows.
- Reviewed the selection for rogue formulas (none).
- Copied the data to a new sheet and tried the same Sum.
**This works correctly!** - Quick summed each 1*20 column in turn (individually they sum correctly).

**Question: What are ALL of the potential causes of such an incorrect calculation?**