Winter 2017/18

Gloucestershire Heritage Hub

BM?

Have you ever looked at an old map and wondered what BM means? At our recent drop in session where we were using historic maps to inspire ideas and memories, lots of visitors wondered what the BM meant. It appeared very often on the old maps we were looking at and was usually followed by some numbers.

 

PH appeared quite a lot too!! (Public House just in case you're wondering). 

All can be revealed - BM stands for Bench Mark. And, of course now you are wondering what is one of those? 

A Bench Mark is a surveyor's mark cut into a wall, pillar, bridge or building and according to Ordnance Survey they are used as a reference point in measuring height above sea level. If the exact height of one BM is known, the exact height of the next can be found by measuring the difference in heights, through a process of spirit levelling.

They are most often found on the corner of a street and usually placed about a quarter of a mile apart. Or at least they used to be. Lots no longer exist because buildings and walls have been demolished or the marks have eroded.

          

This bench mark, situated near the Archives, is according to our Relief Site Manager, Henry, quite unusual because it's cast iron. We wondered if it had something to do with the foundry that used to be on Foundry Street. (On later maps Foundry Street no longer exists and instead Sweetbriar Street has been extended.)

 This bench mark is more usual and is carved into the wall about half a metre off the ground. Very handy for getting a crick in your neck if you are keen to spot one.

 If you would like to find out more about bench marks visit www.ordnancesurvey.co.uk/benchmarks/benchmarks

Or to look at the benchmark database visit http://www.bench-marks.org.uk/

 

 

Comments

Your comments (2 comments)

  • Derek PattensonMay 15, 2023

    Hi.. the metal post is actually nothing to do with benchmarks at all. The arrow symbol is a generic "government property" symbol, known as a Broad Arrow; the benchmark used by the OS is based on this but with a datum line added. The marker actually indicates the location of a cable joint in an underground telegraph cable; versions from Victoria's reign, Edward VII and George V all exist. I know of 9 such markers remaining in Gloucester, though originally there would have been more since they were spaced about 150yards apart along the route of the cable. The "Ft/In" numerals (missing on this post) indicated the horizontal distance in front of the post to the cable, which could be buried anything from 9" to 2'6" or so below ground. The main cable route in the city is the Edwardian Birmingham-Bristol one, but there were later (GR) branches to local destinations. For more information, (including the post illustrated specifically) see gpo-markers.derektp.co.uk/detail?post=525 I'd like to add this image to the record of that marker, with your permission and credited to you; please let me know if that's OK.

  • Kim kennyMay 18, 2022

    Testing to see if comment button works

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