The speed of land vehicles such as cars is measured by how fast their wheels rotate. But in the case of planes, this can be measured by something other than wheels that changes with speed―the air flow which passes across the plane as it flies.
The device which measures this flow of air is called a pitot tube―named after its inventor Henri Pitot.
Pitot tubes calculate airspeed from dynamic pressure, which is found by subtracting the air's surrounding pressure (static pressure)—measured through small holes in the side—from the pressure of air flow into a tube in the front of the device (stagnation pressure).
Three in total: two on the right side and one on the left side. One of the right hand side pitot tubes is a backup.
These are generally located in the same spots where they are located on commercial airliners—be sure to check them out!
HondaJet's first FAA-conforming test model reached a maximum speed of 425 knots (787km/h), exceeding its target performance of 420 knots (778km/h). (March 11, 2011)
The below photograph shows the HondaJet during a test flight. You can see a red rod-shaped device (nose boom) on the tip of the nose.
This nose boom is, in fact, an air data measurement device, and attached to its tip is a pitot tube.
As the pitot tube on the front of the air boom is unaffected by air stream disturbances from the aircraft, flight speed can be measured with greater accuracy during testing.