Want evidence? Here it is. Total precision in design. Crossing reflections (my term) are when 2 angles are the same degree (one up and one down) but start from different centers. Normal reflections start from the same center. The circle is used to keep a close tab on the proper scale set. The vertical arrow should just touch the top of the circle. Have fun and learn something. If you go back far enough there are 2 more 25,25's at the beginning. Just click on the arrow in the upper right hand corner of the chart and "make it mine". Then you can work with it yourself.