How is variable zoom done?

[SEE]

If you have an X52 you can use the Mouse on the Throttle to zoom in/out. You have to map the mouse button (default 5 in game controls menu ) to a switch on the X52. I use the Pinkie button, while I have this pressed the joystick mouse controls the zoom.

Alternatively, using the SST software, map the Mouse control option (in the game controls menu) to a keystroke or button but set that button to 'toggle' on or off. The throttle mouse will control the zoom without having to keep the pinkie pressed .....I prefer to use the pinkie - its very simple and natural on the X52.