Research Concepts RC1500 - Manual (Page 17)

Antenna Setup
17 RC1500B Quick Start Guide
Mount Hour Angle also referred to as the Mount Polar Angle
8. Position the large nuts on the Mount Hour Angle adjustment threaded rod so that the
Hour angle is zero. Use built-in protractor shown in Figure 19.
Figure 19 – Set Hour Angle to Zero Using Long Threaded Rod