G700s as well as the majority of mice from Logitech are equipped with infrared scroll. The scroll wheel has small grooves like a bicycle spokes. An infrared diode projects through these spokes and is captured by the sensor on the other side. The movement of the spokes on the wheel will in turn obscure the infrared beam generated by the diode and based on the obscure sequence, the processor will know whether you are scrolling back and forth. Because there is no physical contact, the durability of scroll is expected to be very high, I have used Logitech M505 so I can guarantee this.
from trusted user reviews