For instance, I utilize Retul. Their fore/aft measurement is titled “Knee Forward of Foot” defined as: The average of each stroke's difference between the horizontal positions of the knee and foot when the foot is in the forwardmost position where a positive number represents the knee being more forward then the foot. The stated range for a road bike fit is between 0 and -10mm as measured by Retul assuming proper sensor placement (a big assumption based on some of the marker placement I’ve seen).