# Calculate True Bearing From Magnetic Bearing

If the magnetic declination at a place at the time of observation is known, the true bearing of a line can be calculated from its magnetic bearing and vice-versa.

## Determination of True Bearing From Magnetic Bearing Rules

The following rules are applied to determine the true bearing if the magnetic declination is known:

### 1. If Declination is East

- True Bearing(T.B) = [Magnetic Bearing(M.B) + Declination]

### 2. If Declination is West

- True Bearing = [Magnetic Bearing – Declination]

## Calculate True Bearing From Magnetic Bearing- Example

** Example:** The magnetic bearing of a line OP is 89°45՛. Determine the true bearing if –

**a)**The magnetic declination is 5°30՛ E.

**b)**The magnetic declination is 4°15՛ W.

** Solution: a)** In fig. (

**i**) True Bearing = (Magnetic Bearing + Declination) = (89°45՛ + 5°30՛) = 95°15՛.

**b)** In fig. (**ii**) True Bearing = (Magnetic Bearing – Declination) = (89°45՛ – 4°15՛) = 85°30՛.

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