A closed compass traverse PQRS is run with prismatic compass in a clockwise direction
| Line | Fore bearing | Back bearing |
| PQ | 50° 00′ | 230°00′ |
| QR | 170° 00′ | 350°00′ |
| RS | 230°00′ | 50°00′ |
| SP | 310°00′ | 130° 00′ |
calculate the included angles of the traverse PQRS and apply the Usual check
SOLUTION :
| Line | Fore bearing | Back bearing | Difference |
| PQ | 50° 00′ | 230°00′ | 180° |
| QR | 170° 00′ | 350°00′ | 180° |
| RS | 230°00′ | 50°00′ | 180° |
| SP | 310°00′ | 130° 00′ | 180° |
From the above table it is observed that F. B and B.B difference of all the Lines are 180° so there is no local attraction and no correction is required and they are shown in the Following figure
Calculation of interior angles with reference to above Fig
interior ∠ P = B.B of SP – F.B of PQ
= 130°00′ -50°00′
=80°00′
Interior ∠Q= B.B Of PQ – F. B of PQ
= 230°-170°
=60°
Interior ∠R = B. B Of QR – F.B Of RS
=350°-230°
=120′
interior ∠S =360° – (F. B Of SP- B.B Of SR )
= 360°- (310°-50′)
= 100°
check:
sum of interior angles =∠P+∠ Q +∠R+∠S
=80°+60°+120°+100°
=360°
should be Equal to ( 2N -4 ) x 90. ( N= no of angles )
= (2×4-4 ) x 90
= 360°
Hence calculated Interior angles are correct