Found using WP 2.6 and CyStats 0.9.4. A divide by 0 warning appears on the CyStats's Index page after deleting database data.
Steps to reproduce:
1. Go to CyStats > Options, scroll down and select the following three checkboxes:
* Delete live database table.
* Delete static database table.
* Do you really want to do this?
2. Click the Delete button.
3. Go back to CyStats > Index to confirm that data are cleared.
Results: Data are cleared, except that near the top of the page I get this warning:
Warning: Division by zero in /[my-path]/wp-content/plugins/cystats/admin/index.php on line 283
Note that this warning does go away as soon as a hit occurs (such as a bot).