
This button is actually used to trigger gesture commands. There's a third thumb button, built into the rubber surface of the thumb cradle. Truth be told, I wish the primary scroll wheel was more like the thumb wheel. The result is a very nice, extremely smooth scrolling action that works quite well if you have a less-than-dexterous thumb. The rotation is slow, and the wheel feels like it has some weight to it. This thumb-wheel provides side scrolling capability, which is sometimes nice to have, but what really stands out about the thumb-wheel is how it feels. 9 ( at Amazon) than the thumb paddle found on the Roccat Tyon ( at Amazon). It's more like the thumb wheel found on the Mad Catz M.O.U.S. There thumb cradle sports forward and back thumb buttons and a second scroll wheel. I do, however, wish that there were some way to adjust the threshold point between ratcheting and free scrolling, as I would occasionally attempt to scroll a tad more quickly than usual and suddenly zoom through to the end of a document without meaning to. The scroll wheel also has a speed-adaptive scrolling feature that switches from ratcheting to free spinning when you flick the scroll wheel faster than an incremental scroll, without having to tap the button.

It's a feature that is particularly helpful when scrolling through long documents. The right and left buttons and clickable scroll wheel are in the usual spots, and Logitech adds a button that switches the scroll wheel between a ratcheting action to a free-spinning scroll. The sides sport a polygonal, faceted texture, which looks interesting and provides a reasonably comfortable grip.

The black-on-bronze color scheme is nice enough, but appropriately sedate-it will fit in nicely in a conservative office environment.

The mouse is constructed of plastic, with a rubber layer covering the palm rest and sides. There are some definite similarities to the Logitech M705, aside from the thumb cradle. Measuring 3.4 by 5 by 2 inches (HWD), the MX Master is meant for right-hand use, molded to fit the average hand, with the protruding wing of a thumb cradle on the left side.
