The FSAS SPAN, SPAN CPT and SPAN SE support the following inputs from a wheel sensor. Their definitions are as follows: Signal A/ODO_A: This is a quadrature output signal from the wheel sensor. This signal is used to calculate the distance traveled and the velocity of the vehicle. Different wheel sensors will have different pulse or tick counts per revolution. This value must be set using the SETWHEELPARAMETERS command. Once this has been set, the cumulative tick counts can be found in the TIMEDWHEELDATA log. Signal A Inverted/ODO_AN: This signal is the inverse of Signal A. It is designed to improve signal transmission. Signal B/ODO_B: This is the second quadrature output signal from the wheel sensor. This signal is 90 degrees out of phase with Signal A. When combined with Signal A, it is used to determine the direction of travel. Signal B Inverted/ODO_AB: This signal is the inverse of Signal B. It is designed to improve signal transmission. For real-time operation, a minimum of Signal A is needed when using a wheel sensor. Our SPAN products use the magnitude of the change in tick counts from the TIMEDWHEELDATA log to calculate velocity and distance traveled. Therefore, the direction of travel is not needed. However, if you intend on post processing the data, a minimum of Signal A and Signal B are needed. Our Waypoint post processing software looks at the cumulative tick count field in the TIMEDWHEELDATA log to determine the velocity and distance traveled. It also determines the direction of travel from this value. If the number increments, it is traveling forward. If the number decrements, it is traveling backwards.