A steel plate leveler is a machine used to flatten and level steel plates. The leveler uses a series of rollers and hydraulic cylinders to apply pressure and bend the steel plate until it is flat. 

This process is important for ensuring the accuracy of steel plates used in construction, manufacturing, and other industries where precise measurements are required. Steel plate levelers can handle plates of varying thicknesses and sizes, and can be operated manually or automatically. They are often used in conjunction with other machines, such as shears and presses, to create finished products from the flattened steel plates.