BikeCAD Pro displays three different seat stay length dimensions. In the Tubing tab of the Dimensions dialog box we have Seat stay length and Seat stay length 2.
Seat stay length is measured from the rear axle to the point where the centerline of the seat stay intersects the surface of the seat tube.
Seat stay length 2 is the distance from the rear axle to the intersection of the seat stay centerline and the seat tube centerline.
In the Stays (Auxliary view) tab of the Dimensions dialog box we have another dimension, also called Seat stay length. This is the distance between ends of the seat stay measured along the centerline of the stay in the auxiliary view.