Mathematics for IGCSE & O level - Pythagoras' Theorem And Trigonometry (Section 3 - No. 12)
The angle of elevation of a point B from point A is the angle between the horizontal plane and:
A line of sight below the horizontal plane
A line of sight above the horizontal plane
The vertical line
The distance AB
Explication
The angle of elevation is the angle from the horizontal plane upwards to the line of sight.