The angle of elevation and angle of depression both are measured with
Angle of elevation:
The angle of elevation is an angle that is formed between the horizontal line and the line of sight.
Angle of depression :
The angle of depression is "an angle formed between the horizontal line and the line of sight when an observer looks downwards at an object is known as an angle of depression"
The angle of elevation and angle of depression is measured with the line of sight that is always horizontal.
Hence,angle of elevation and angle of depression both are measured with horizontal axis.