Hi JNW,

You can easily restrict the entry of positive numbers in a cell using data validation in Microsoft Excel. Here are the steps:

1. Select the cell or range of cells where you want to restrict the entry of positive numbers.
2. Go to the Data tab in the ribbon and click on Data Validation.
3. In the Data Validation dialog box, select "Custom" from the "Allow" drop-down list.
4. In the "Formula" field, enter the following formula:
   Formula:

   =A1<0 

   (assuming the cell you selected is A1).
5. Click on the Error Alert tab and enter a suitable error message, such as "Please enter a negative number".
6. Click OK to close the Data Validation dialog box.

Now, if you try to enter a positive number in the selected cell or range of cells, you will see an error message and the entry will be rejected.