It is one of the tools of the structor (the mason), often depicted with other of the instruments on funerary reliefs of the Roman period, as in Pompeii itself (relief of Diogenes structor). This exemplar has one of its arms furnished with a base for support and the extremities are modelled; this peculiarity, sometimes seen also on the funeral reliefs that depict this instrument, leads us to conclude that it was used also for tracing the profiles of cornices.