Concept: We know the relationship between FB and BB Back bearing (BB) = Fore bearing (FB) ± 180°. +ve sign is used if FB is less than 180° and –ve sign is used if FB is more than 180°. Included angle = Fore Bearing of next line - Back Bearing of the previous line Calculation:
Fore Bearing of AB = 150°15' Included Angle ABC = 110°30' Back Bearing of AB = 150°15' + 180° = 330°15' Included angle ABC =F.BBC−B.BAB 110°30' =F.BBC - 330° 15' F.BBC = 440°45' F.BBC = 440°45' - 360° = 80° 45' Note: If the included angle is negative, then add 360°. If the included angle is greater than 360° then deduct 360°.