David Evan’s question earlier today over the flush bracket benchmark is interesting and significant to the blog. Both he and I knew well what it is and what it was used for; I’m a bit of a Ordnance Survey anorak and look out for them wherever I go. The one David identified was indeed on the library in Lichfield, and was the sign of a major reference point. The ‘Flush Bracket’ in question actually has holes in which to mount the surveyor’s measuring equipment.
Minor benchmarks are often just carved in the brickwork of permanent structures, or on posts, while primary points can be on the familiar trig pillar or a location like a church spire. Sometimes that lone, square post in the middle of a field is actually a monument for a benchmark.
There are a variety of different benchmarks, brackets and studs in use; their identification and usage is explained in this great link supplied by Peter ‘Pedro’ Cutler, who’s also a bit of an OS aficionado.
The system is little used now, with the advent of modern surveying techniques, but is still employed by some civil engineers, builders and architects on occasion.
If you’re wondering if there’s a way to find benchmarks and suchlike from mapping, here’s how. On old maps, the carved symbol above is employed on the map for minor ones and brackets, and the familiar triangle with a dot in for monuments, or primary references on buildings. The small crosses with a number next to them are spot heights. The example being a 1:2,500 scale map section of Brownhills Central from 1919.
For locals who may be interested, there used to be a flush bracket on the Shire Oak Pub, but think it may have been removed. There are plenty of minor benchmarks still extant about the town, though.
There’s a database online of benchmarks, brackets and monuments. Go and have a look.
Once, it was an offence to remove or tamper with any such reference. Learning to carve the arrow symbol was part of the Ordnance Survey’s surveyor training; the wall at the back of their old premises in Southampton was covered with hundreds of practice benchmarks.
The map I took the above section from has lots of benchmarks on it – why not take a walk tomorrow, and see if you can find some? I include the whole sheet below for you to peruse.