1. Apparatus for tracking the movement of a longwall coal shearer along a desired path along a longwall coal face of the type which travels over rails and is driven by means of a drive gear and toothed drive rack, said apparatus comprising: a continuous rectangular light beam image; optical tracking means carried at one end of said path including light transmission means for converting said rectangular light beam image into separate alternating continuous horizontal and vertical rectangular light beams and alternately transmitting said horizontal and vertical light beams down said path; retroreflector means carried by said shearer for receiving said alternating continuous horizontal and vertical light beams; said retroreflector means including means for converting said alternating continuous horizontal and vertical light beams into a series of discreet horizontal and vertical light beam images at periodic intervals along said path which are reflected back to said optical tracking means; said retroreflector means reflecting said horizontal and vertical light beam images responsive to the vertical and horizontal deviations, respectively, in the movement of said shearer and corresponding displacement of said retroreflector means from said desired path as carried thereon; said optical tracking means including optical receiving means receiving said horizontal and vertical light beam images; and recording means for recording said images as a function of the position of said shearer along said path for viewing so that the travel of said shearer may be corrected.