; BCRA Grade 3 specification file ; tape error ; 95.44% of readings are within 0.5m (2 S.D.) *sd length backlength 0.25 metres ; compass error ; 95.44% of readings are within 2.5 degrees (2 S.D.) *sd bearing backbearing 1.25 degrees ; clino error ; 95.44% of readings are within 2.5 degrees (2 S.D.) *sd gradient backgradient 1.25 degrees ; station position error ; 95.44% of positions are within 0.5m (2 S.D.) *sd position 0.25 metres