References
Sam Brown, 1975, All About Telescopes 2nd edition, Edmond Scientific 1975, page 3
Harrie Rutten and Martin van Venrooij, Telescope Optics, Willmann Bell 1988, page 66
Harrie Rutten and Martin van Venrooij, Telescope Optics, Willmann Bell 1988, page 67
Russell Porter, 1935, Fundamentals in the Design
of Telescope Mountings; Rigidity, Amateur Telescope Making Book One,
Albert G. Ingalls Editor, Scientific American, 1981, page 130