... One way (" polar coordinates ") uses the length r of the line OP from the origin to P (i. e. the distance of P distance to the origin) and the angle that line makes with the x-axis. ... Look again at the surveyor's telescope: the direction to which it points is completely specified by two angles--its azimuth f , the angle by which its base is rotated on a horizontal table-- and its elevation l (small Greek L), the angle by which it is lifted above the horizontal (if it looks down, l is negative). ...