A month in the life of an Ordnance Survey Benchmark bagger

A couple of years ago there were stories in the news about young people, and some not so young, stepping in front of traffic and falling off cliffs whilst blindly following their mobile phones in the hunt for Pokémon.  “How foolish!”, I thought.  However, I now find myself wandering the streets, phone in hand, searching – sometimes fruitlessly – not for Pikachu and its chums but for elusive signs of a bygone technology.

I have become mildly obsessed with finding Ordnance Survey Benchmarks.

https://www.ordnancesurvey.co.uk/benchmarks/ explains what benchmarks are:

Ordnance Survey Bench marks (BMs) are survey marks made by Ordnance Survey to record height above Ordnance Datum. 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.

Most commonly, the BMs are found on buildings or other semi-permanent features. Although the main network is no longer being updated, the record is still in existence and the markers will remain until they are eventually destroyed by redevelopment or erosion.

I’ve been aware of BMs for a long time. Occasionally I’d spot one and I suppose I did know they had something to do with measuring or surveying or something-or-other but I’d never realised how many there were and what a huge effort it had taken to create and manage the network.

A short evening walk had piqued my interest in how the local area had developed in the last century. Looking at old OS maps on the National Library of Scotland webpage I noticed how many BMs were marked.  I tweeted about my observations and was surprised to receive a reply from the OS telling me about the legacy list of BMs. Good grief! There’s over half a million of them . . . . .or, at least, there were although they’ve not been maintained for 50 years and many have been destroyed.

Not only is there a csv file containing every single Benchmark (apart from the Fundamental ones which are still maintained by the OS and therefore, I presume, a possible source of income) but they are also viewable as an overlay on OSMaps (Tick the Benchmarks box under Places).  Wherever I am, so long as I have a data connection on my phone, I can bring up a local map which shows the position of every benchmark.  Touching the benchmark icon brings up a description of where it is.  You do not need to be a paid subscriber to OSMaps to see the benchmarks overlay or to use the basic mapping or aerial view.

Unfortunately, this overlay is not available on the OSMaps mobile phone app.  I have asked the OS about this but it sounds like it’s a long way down their development priority list.

As a newcomer to the world of benchmark bagging there are plenty to find everywhere I go.  I’ve got into the habit of having a quick look at the map before I go somewhere so that I know which benchmarks I’m likely to be able to find.  The description is usually helpful:


However, there are some parts I still do not understand.  For example, what is the “ANG” referred to in this one?  BLDG NO63 HAMILTON ST NE FACE N ANG

The wall faced NE-ish but I can’t figure out what angle could be referred to.

I’ve learned to look round the corner: FL BR G3955 NO138 PARK RD NORTH SE FACE S ANG

Definitely on Duke Street not Park Road North


In the last month I have found and photographed 29 benchmarks.  Most have been cut marks, ie the distinctive arrow head, but there has been 1 flush bracket; the Park Road North / Duke Street one above.  I had always assumed that the flush bracket I saw on a hill-top triangulation pillar, ie trig point, was a key part of the trig point.  In my ignorance I had no understanding of the different purpose of a trig pillar (surface distance) and a benchmark (height above Ordnance Datum / sea level).  All those photographs I’ve taken of trig pillar flush brackets over the years can now go into my Benchmark collection!

Ah, yes, the collection…….

What I would like to do is catalogue every benchmark I have found.  It needs to be ticked off a list and have the date of discovery noted along with a photograph and a description of the condition of the mark.  Of course, it is equally important to record the ones which I’ve looked for but couldn’t find…… and there have probably been over 20 over those, so far.

I’ve dallied with a few different ways of recording my finds.  An online map would be perfect but I’ve not yet found a way that seems to do the job in the way I would like.  I am geotagging my photos, so it should be possible to put them on a public online map, but I’ve not yet found the best way to do it.

I could also upload them to Geograph but I’d like a simple way to only display the BM photos on a map and I’m not sure if Geograph can do this.

Of course, no hobby – however strange – is ever new on the internet and I know there are communities of BM-baggers keeping and publishing their own records.  I’ll probably contribute to https://www.bench-marks.org.uk/.

You may have noticed that I’m quite passionate about these weird wall-scratchings.  People collect all sorts of odd things so I mustn’t beat myself up over being a Benchmark Bagger.  It doesn’t hurt anyone and it gives me a good excuse to go for a walk at lunchtime or in the evening and see what I can find.  I’m also enjoying looking at old OS maps to work out where a missing BM used to be.

It’s free, it’s harmless and it’s interesting …. and if you’re reading about benchmarks for the first time I bet you’ll have to have a little peak at OSMaps to see where your nearest one is.

This entry was posted in Uncategorized and tagged , . Bookmark the permalink.

15 Responses to A month in the life of an Ordnance Survey Benchmark bagger

  1. Fellbound says:

    I have always loved coming across benchmarks. I think it’s the actual ‘arrow’ mark design. Reminds me of the cartoon prison uniforms from comics in my childhood. I have always been surprised by the number of outdoor folk ie regular OS map users who didn’t know what they were. As for collecting them? That way madness might lie. 😂


  2. louse4 says:

    Well, I read all the way to the end, so that must have been interesting.
    And I might peak at the OS maps…


  3. John Jocys says:

    You might also find it interesting to keep an eye open for old (ancient?!) Boundary Stones and other boundary markers. Oh, and old Mile Stones.


  4. AlanR says:

    It does get to you. Even Sheila is now constantly looking and acting strange at street corners.
    And I can only assume ang is angle but there must be a list of abbreviations somewhere.
    I would like to map my finds also so keep me informed of anything you think is good.
    Thanks for getting me interested. Mmm

    Liked by 1 person

  5. As someone who also (just this year) discovered benchmarks (I log all mine, when I have time, on bench-marks.org) I’ve a few more clues about the terse descriptions (I figure they only had limited space to record descriptions, hence the notation format).

    “BLDG NO63 HAMILTON ST NE FACE N ANG” means number 63 on Hamilton St, obviously, and the BM is on the NE face, close to the N angle – so you know the face of the building it’ll be on, and at which end, in this case the northern corner, rather than the eastern corner, of that face.
    I think PRODN is best read as “projection”, indicating following a line from somewhere. There’s a rivet near to me described as “NBM RIVET NW SIDE BEESTON CANAL PRODN E FACE HOS” and it’s on the NW side of the canal in line with east face of a row of houses across from the canal.

    The rural ones seem much harder to find, and I’m amazed how people have found some of them.

    Most abbreviations can be found at https://www.ordnancesurvey.co.uk/resources/maps-and-geographic-resources/map-abbreviations.html

    I’ve also created a website with all of the known BMs marked on it at https://benchmarks.for-our.info/map.html – as you can filter by BM type I find it quite useful when out, and it works okay on a smart-phone (if you use Chrome). It’s got Trig points as well – they are often paired obsessions 🙂

    Happy hunting!

    Liked by 1 person

  6. Judith says:

    Thanks Mike. That adds a few more pieces to the jigsaw puzzle. I like that map. I’ll have a better look when I get back from tomorrow’s walking / camping trip (or maybe whilst camped on the side of a Welsh hill if I can get a signal!)


  7. lizziwake says:

    I just love the way that knowledge surfaces when you need it. Reminds me of the saying: when the student is ready, the teacher appears. Twitter makes that so much easier 😉

    Liked by 1 person

  8. Pingback: Bracken, Bivi and Benchmarks | Around the hills

  9. gm7something says:

    They are addictive, I’ve cycled my immediate area searching (using the OS database), many have ‘disappeared’, my wife now dreads the ‘wow, benchmark’ as we travel on a new road…
    Every road, building corner gets scanned…
    Mike’s map mentioned above will be handy for random visits…
    I use the OS locate app, then email the OS reference and a description to myself and check against the database, with a notebook backup…
    Now if that map could me made into an app..
    Keep searching!

    Liked by 1 person

  10. Pingback: The Walk Part 1: Carvings – The Glossop Cabinet of Curiosities

  11. Conrad Wass says:

    I’ve lived in my house for six years and only just realised there’s one chiselled low down on the front of my house. I looked up the map, and also found your blog, so here I am!
    An interesting read, I’ll be looking out for them everywhere I go now too!
    Conrad, Huddersfield.


  12. Linda burt says:

    Got another for you 5 main street huncote. I wondered what it was now i no thanks


Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s