Since the measurement is relative to the horizon, the measuring pointer is a beam of light that reaches to the horizon. The measurement is thus limited by the angular accuracy of the instrument and not the sine error of the length of an alidade, as it is in a mariner's astrolabe or similar older instrument.
Since the measurement is relative to the horizon the measuring pointer is a beam of light that reaches to the horizon The measurement is thus limited by the angular accuracy of the instrument and not the sine error of the length of an alidade as it is in a mariner's astrolabe or similar older instrument