Exact straight line by special square
■ If AB ≠ BC Such case, we need 7 bars. ( cf. Exact straight line by general square. ) AB = BC condition causes the simplicity. (points A, C are shared by Green bars.) ■ AC // M'M is very important trick In above sample, M is the middle point of CD. i.e. ratio is 0.5. But, any ratio is OK, of course. △CHA ∽ △MGM' --- so, HA // GM' --- so, HA // M'G' ■ Imai's Low of cosines frame. This tool is educational for students. I named this method "Imai's Low of cosines frame", as a memento. This method is simpler than "Hart's Inversor" or "Hart's A-frame" methods, I think so. But as a result, this tool is same as Hart's Inversor apparatus. That is, different approach, different proof.