Scala's account is supported by Manetti, who claims that Filippo used
this same procedure when vaulting the Ridolfi Chapel. In this experiment
the capomaestro used a cane that was fixed at one end and 'circled upwards,
gradually narrowing as it pressed constantly on the bricks on its unfixed
side'. This device anticipates the modern-day 'trammel' used by bricklayers
in order to set out circular walls. The trammel consists of a horizontal
wooden plank that pivots on an upright metal bar fixed at the centre of the
wall's curvature. Describing an arc as it rotates round this axis, the plank
indicates the position in which each individual brick should be laid.