The EM400 is a rugged, blade-mounted, electronically adjustable mast that provides an electric motor-operated lead screw for positioning the height of the LR400/410 laser receiver from the cab of mobile machinery. The EM400 is used with the M4 heavy-duty shock mount for mounting over the blade's cutting edge. Contact us for more information on this product! Sheroz Earthworks. GPS Machine Control Specialists.