How to make a dotted or dashed axis.

GraphPad Prism does not really let you choose the style (solid, dashed, dotted) of the axes, but if you are a bit tricky you can make it happen. Follow these steps.

1. Go to the first tab of Format Axis, and choose to hide the axis that you want to be dotted or dashed. Uncheck the option to show a scale bar.
2. Double click on the other axis to bring up Format Axis.  
3. At the bottom of the dialog, enter a coordinate (probably 0.0) and check the option for a grid line to replace the axis. 
4. Click the "..." button (or the gear button in Prism Mac) to bring up the dialog that lets you fine tune additional labels and grid lines.
5. Choose the style (dotted or dashed) and thickness you want. 
6. OK twice.