Tractors with multiple 'road gears' often have tachometers with more than one speed scale. Therefore, the Austro-Hungarian fighters were equipped with large and prominent tachometers in the cockpit. Aircraft tachometers have a green arc showing the engine's designed cruising speed range. Starting this year, tachometers were electronically driven. Tachometers on every axle of the unit provide for Wheel Slip/Slide Protection. Tachometers are used to estimate traffic speed and volume (flow).