The Hornsby Test Line consists of three fairly prominent trigonometric markers. Technically, these are not Trigonometric Stations (TS), but Permanent Survey Marks (PM) – which are generally small metal discs in the ground. But these look more like traditional trig stations, which are positioned fairly close to each other in a perfectly straight line.
Nearest to the road is PM 58063, with a concrete base topped by a plastic cone.
Fifty metres to the north is PM 58064, which has the same design.
Another 50m to the north is PM 58065, which has the same concrete base, but also a metal mast and vanes.
Getting to the Hornsby Trig Line
The three trigs (or to be precise, permanent survey marks, are at the end of Murralong Road in Mount Colah, in Sydney’s north. There’s a track between the three trig points.