; BCRA Grade 3 specification file ; tape error ; 95% of readings are within 0.5m (3 S.D.) *sd length 0.15 metres ; compass error ; 95% of readings are within 10 degrees (3 S.D.) *sd bearing backbearing 3.33 degrees ; clino error ; 95% of readings are within 10 degrees (3 S.D.) *sd gradient backgradient 3.33 degrees ; station position error ; 95% of positions are within 0.1m (3 S.D.) *sd position 0.15 metres