The leader climbed the route and set up an anchor. One rope was passed through the anchor screw gate and brough back to the belay position where it was clove hitched to the climber using another screw gate. The error made was that the clove hitch screw gate was not passed through the loop of rope created by the figure of eight when tying in to the rope at the start of the climb, but was clipped between the figure of eight and stopped knot. The second climber noticed this error upon completing the route but if they had fallen and the anchor was weighted then there was a significant risk the stopper knot may not have held as the tail was not long.