I'm a bit lost when it comes to measuring tail angles. The SOP has an illustration showing and angular measurement between the first sickle feather relative to the back, which in the case of the illustration is horizontal. So do you measure the angle between the first sickle feather or the center line of the tail? Also, in the case of birds with a continually sloping back, like Dominiques, at what point in the back do you choose to do the measurement? Also what does it mean when a bird has a break in the tail?