1. Click on the y-axis or data labels
  2. Right-click and select Format Axis... or Format Data Labels...
  3. In the right-hand pane, click on the "Label options". It looks like a bar graph
  4. Click >Number to expose more detail
  5. In the format Code textbox
    1. Remove all contents inside of that textbox
    2. For less detail, enter:    0,, "m";-0,, "m";"-"  

    3. For moderate detail, enter:    0.0,, "m";-0.0,, "m";"-" 

    4. For a lot of detail, enter:   0.00,, "m";-0.00,, "m";"-"  



Here's how it looks