A perpendicularity verification device is provided for verifying perpendicularity of a concrete test specimen in a testing machine. The device comprises a unitary planar sheet. The sheet has an elongate vertical straight side edge and a horizontal straight bottom edge. The side and bottom edges are perpendicular to one another. A corner notch is provided between the side and bottom edges. In use, the bottom edge rests on a platen of the testing machine so that the notch circumvents a retaining cup of the testing machine and the vertical edge rests against the test specimen.