Airspeed indicators come in 3 1/8 inch and 2 1/4 inch format. There are airspeed indicators and true airspeed indicators that allow you to enter the outside air temperature and the altitude, thereby indicating the TRUE airspeed. Most airspeed indicators have range markings with flap speeds (white), structural cruise speeds (green), maneuvering speed (blue), smooth air cruise speed (yellow) and Vne (red line). Some have internal lighting. Different aircraft have different speeds, so be sure and select the one for your aircraft.