http://wikiless.i2p/wiki/Triangulation_station?lang=en
They look like a small circular manhole cover, with the epoxy inside. [ 3 ] Stainless Steel Rod (S/S Rod) [ edit ] They are small concrete bricks, with a stainless steel rod fixed in it, they are used as bench marks. [ 3 ] Others [ edit ] There are many more other types of surveying marks in Hong Kong, such as staples, PVC pipes, or even as simple as a nail. [ 3 ] Classes [ edit ] Trig points and Traverse Stations in HK have a 2 class class system, they can be identified by their numbers....