An improvement to a measuring table for fabricated plate products, such as sheet metal and the like. A measuring table having legs for support of flat table surfaces with opposite sides and ends is equipped with a straight reference gauge extending squarely across the table surfaces near one end and a slot extending at right angles to the straight reference gauge. The improvement to such a measuring table comprises a linearly stationary yet pivotal contact mounted in the slot adjacent to the reference gauge, a pivotal contact movable in the slot by a carriage slide mounted to the underside of the table, and a microprocessor operatively connected to the contacts to receive, store, process and display the measurements therebetween. The method of this invention comprises the steps of spreading the contacts to accommodate between them a plate laid on the table surface, positioning one corner of the plate against the linearly stationary yet pivotal contact, sliding and pivoting the movable contact against an opposing corner to generate a first measurement of the plate's diagonal, repeating the above steps to generate a second measurement across another diagonal, and comparing the deviation between the first and second measurements to a predetermined acceptable limit. Those plates having excessive deviations between the diagonals are rejected as out of square.