Drawing Scale is a tool box I have permanently docked.
In any MicroStation based application press Ctrl + T to open the Toolboxes dialog.
To open Drawing Scale scroll down and tick the box, click OK:
I turn off Sub Unit and ACS Scale as I rarely use them, then just dock at the top or bottom of the application window.
The Working Units are a display attribute, changing them does not affect the size of elements, just how the units of measurement are displayed so it is easy to switch between units as appropriate to the task at hand.