So I was wrapping up a solid week of adventuring in Tasmania and it was time to head to Launceston airport. To get there I drove through Campbell Town. A lovely place with an interesting history. There are two trig point caches so of course I checked them out. One is a marker set in a base for a monument (a sundial) commemorating the transit of Venus which is when the planet Venus passes directly between the Sun and Earth. It’s quite a sight apparently! NASA visited the town some years ago to witness this. I don’t know why Campbell Town is the place to be for observing celestial goodness but the next event is December 2117. While this trig sits on a corner of the base of the monument, a U.S. Survey Bench Mark sits on another corner of the base and has its elevation above sea level listed at 654.77 feet.
I went to the local museum and information office and asked about the bench mark but they knew nothing about it. They were super helpful though on other matters and a pleasure to chat to. The old book store nearby is a real gem but that’s another story.
Here’s some nerdy information on bench marks.. Standard Survey Marks have a known horizontal and vertical position whereas Bench Marks only deal with vertical positioning. A BM is a point of known height above or below Mean Sea Level. This is called a Reduced Level and is determined by a survey method known as Levelling.
A long time ago a Bench Mark was made by cutting a ‘bench’ out of a base of a trunk of a large tree. A blaze would then be made above the bench with relevant information. I haven’t found one these ol’ school bench marks but I’m planning to track some down soon(ish).
Back to the U.S. BM. I’m unlikely to see another one of those so it was a great discovery. I have little interest in visiting America and will probably only do so if a unique opportunity was to present itself.
If you want to see one of these and you happen to be in Tasmania, head to Campbell Town
