Align the edge of your compass along the line that connects A and B.
Turn the bearing so that it points toward North parallel to the grid lines. Name this angle α, assume α=231°.
Add magnetic variation ν if applicable. Assume ν=3°.
Hand your compass before you and turn your body for angle τ until the magnetic needle with N on the arrow is aligned with the arrow that is drawn in the bearing. Assume τ=23°
The magnetic bearing will be