Bug: Whe you create a file ncluding a discontinuous axis made with Prism 4 and then open it using Prism 6 or 7, you may not be able to get the numbering you want.

When you created an axis with two segments (a discontinuous axis) with Prism 4, it included an option on Format Axis:  "Plot only one tick on this segment". That option was removed in Prism 5, When  Prism 6 or 7 open such a file, it can get confused and not let you adjust the range or numbering on that axis segment. 

To work around this problem, go to the data table, click New ... Graph of existing data. Then use magic to improve its appearance. Then adjust as needed.  You won't be able to adjust the axis segment limits and numbering on the graph made with Prism 4, so you will need to create a new graph.