Wheel Mouse Volume Control – VOLUMOUSE.EXE
Volumouse.exe installs with Volumouse by NirSoft. This utility lets you control the sound volume on your PC by scrolling the wheel on your mouse. Scroll forward or up for louder, scroll backward or down for lower. The wheel on your mouse will perform normally but is switched to control volume by pressing the ALT key on your keyboard. If you want this option to be available to you, leave this file in place.
More information can be found at http://www.nirsoft.net/utils/volumouse.html.
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NirSoft