Elevation
The elevation angle describes how "high up" the pigtails are. It is defined as the angle between the horizontal plain through the head centre and the line connecting the pigtail origin to the head centre. Note that the head centre is defined as the midpoint of the line through both ears.
Elevation angles normally range from -20 to +60 degrees, although higher values do occur. Figure d shows a set of three pigtails, at 75° elevation each.
fig. a: -10° elevation
fig. b: 10° elevation
fig. d: 75° elevation