Instrument and method for measuring flatness using linear light source

The invention discloses an instrument for measuring flatness using a linear light source. The instrument comprises a transmitting device and a receiving device. The transmitting device comprises a base and a transmitting part positioned above the base. The transmitting part is connected with a base bearing, and the outer surface of the transmitting part is embedded with the linear light source which emits light in parallel to the horizontal plane. The receiving device comprises a base with the same height as the base of the transmitting device and a height difference measuring part above the base, a plurality of uniformly distributed scale lines are arranged on the surface of the height difference measuring part, and the zero scale line is as high as the linear light source by taking the horizontal plane as a reference. The invention also discloses a method for measuring the flatness using the linear light source. The instrument is simple in structure, the method is convenient to operate, whether any two poin