This is the follow-up task for the task "Create an About dialog for the scale bar plugin". It's highly recommended to complete the about dialog task before starting this one.

The scale bar should receive a configuration dialog where the user can enable and disable the scale below the scale bar.

The scale feature needs to be implemented as part of this task. The scale (i.e. a value of the form "1:2 000 000") should get displayed below the scale bar as part of the scale bar info box (see http://en.wikipedia.org/wiki/Scale_%28map%29).

The configuration dialog should just provide a simple checkbox which would look like this:

[ ]  Display scale

Have a look at

http://techbase.kde.org/Projects/Marble/OnlineServices

and at the existing Online Plugins. The Wikipedia plugin has got a configuration dialog  that you can use as a "template".

For the actual formula to calculate the proper scale value you can get some help on the marble-devel mailing list or the #marble IRC channel if needed.