On-screen ruler has many options that allow you to customize the programme to your needs.  To access the available options, simply right-click anywhere on the ruler or use the Ctrl+O key combination.

A dialogue box allowing you to customize various aspects of the interface appears when you right-click the ruler.  Edit the options, as described in the following pages, and see the changes reflected immediately.  Note that these options are persistent; that is, the programme "remembers" the options the next time you start it up.  Consequently, you do not need to remember to save your changes, since they are automatically saved when the programme exits.