the central full span truss is formed by 2 'cruck' blades joining at the top centre. They were obtained from the same tree with appropriate curve and dimensions being cleft with wedges down its heart and trimmed with adzes. The apex is scalloped so that a quatrefoil is formed between crucks and diagonal struts. The purlins are tenoned into the face of the crucks (as opposed to being laid on top in later buidings, so they needed to know what order to erect it all!