I newly started to build my avon chassis and i realized that the tubes marked with red arrow into attached picture are not match each other.They have 2 cm diffrence according to my calculation from jim's book.Thats why the tube pointed green arrow does not have 90 deg. to bottom rail. Is this true?
Rescued attachment chassis.JPG

I've made it 90degr. But my frame is as the build growes less tiger.