Replaced several of these in an 811B and it is now fully operational. Davtron does not supply instructions however it is pretty straightforward: 1) disconnect power including the backup battery 2) remove the four screws holding the front panel in place. gently remove front panel. 3) carefully pry out inoperative digits (you may have to remove an edge display to get to the middle ones) 4) make sure leads are straight on new digit 5) insert it with pin 1 (might have a dot) towards the top of the unit. gently press in place. 6) install front face plate 7) attach backup battery Then remind your boss how much money and time you saved by not having to ship it out for repair.