Flatness detector

The utility model relates to a flatness detector, comprising an electrically insulating base, the axis of the base is provided with a base through hole, the upper surface of the base is provided with four conductive contact plates at equal intervals along the circumferential direction of the base through hole, the tops of the four contact plates form a plane structure and are located on the same horizontal plane, the lower surface of the base is provided with an accommodating groove, and the accommodating groove is provided with a through hole. A circuit board and a rechargeable battery with the positive electrode or the negative electrode connected with the circuit board are installed in the containing groove, the base is further provided with a switch and three indicating lamps, the four contact plates comprise a substrate electrode and three conductive electrodes, the substrate electrode and the circuit board are correspondingly connected to the two electrodes of the rechargeable battery, and the conductiv