Just to clarify, when you say "interactive scale" do you just mean the zooming in and out feature?
I don't know if you know a lot about programming but there are these things called event handlers. For example the edge of this window has a mouse over event handler which changes the cursor to a little arrow. This text box that i'm typing this response in has a mouse over event handler which changes the cursor again. This window has a keypress event handler which makes the letter "e" appear in this text box when I type the letter.
For example:
on bing maps I can click the middle mouse and nothing happens. When I click the middle mouse several things happen. The mouse goes down (mousedown event). There is a click (onclick event). Then the mouse button goes up (mouseup event).
There is no code handling the middle mouse click event.
There is no code handling the middle mouse mousedown event (provided that the mouse didn't move).
There is no code handling the middle mouse mouseup event (provided that the mouse didn't move).
on bing maps I can double click the middle mouse and nothing happens. When I double click the middle mouse several things happen again. this appears not to change the scale of the map
on bing maps I can press and hold the middle mouse. Then while the middle mouse is held move it. Then after moving the mouse let go of the middle mouse button which changes the scale of the map
middle mouse on mouse down event = Take a picture of the starting position of the mouse
middle mouse on mouse up event = take a picture of the ending position of the mouse
if starting position of the mouse <> ending position of the mouse then
change map scale
end if
In addition to things like dragging and dropping the middle mouse which appear to have an effect on the scale of the map there are keyboard buttons like the arrows which appear to, in certain situations, change the scale of the map. There are many different combinations of events and inputs you can send to the map which either always change the scale or sometimes change the scale.
When I say interactive scale i'm talking about any combinations of clicks, button presses, or other events which will change the scale of the map without doing things like injecting code or scripts or altering memory if the computer or browser in which those inputs, clicks, or events change the scale of the map. I didn't build the interactive map so i'm unable to tell you all the events and inputs which can change the scale of the map. I highly doubt Bing would tell you either.