SecretLeeds - History, culture and architecture in Leeds

The photo shows a well defined bench mark (BM) a couple of blocks above the pavement in about the centre of the photo I took on March 28 2012. The wall is that at St John's church grounds facing New Briggate. A BM is marked there in an 1891 1:500 map in the excellent Old-Maps UK website (as also are the nearby steps). The BM does though looks too well defined to be that from at least 1891 and also the long block that part of the BM is on is not the same as virtually all of the other slabs the wall is built of. It seems likely therefore that this BM is not the original one but it is still a nice one that perhaps has not been spotted by many. The out of focus Blue Plaque on the right commemorates John Harrison 1579-1656.I shall post a close-up view of the BM in my next post.

This photo (taken March 28 2012) is the close-up view of the well defined bench mark.

Whats a benchmark BTW?Am I thinking too literal when I imagine it to be a marker for someone to put a wooden bench against?

WiggyDiggy wrote: Whats a benchmark BTW?Am I thinking too literal when I imagine it to be a marker for someone to put a wooden bench against? The term bench mark, or benchmark, originates from the chiseled horizontal marks that surveyors made in stone structures, into which an angle-iron could be placed to form a "bench" for a leveling rod, thus ensuring that a leveling rod could be accurately repositioned in the same place in the future. These marks were usually indicated with a chiseled arrow below the horizontal line.The term is generally applied to any item used to mark a point as an elevation reference. Frequently, brass or aluminum disks are set in stone or concrete, or on rods driven deeply into the earth to provide a stable elevation point.The height of a benchmark is calculated relative to the heights of nearby benchmarks in a network extending from a fundamental benchmark, a point with a precisely known relationship to the level datum of the area, typically mean sea level. The position and height of each benchmark is shown on large-scale maps.The terms "height" and "elevation" are often used interchangeably, but in many jurisdictions they have specific meanings; "height" commonly refers to a local or relative difference in the vertical (such as the height of a building), whereas "elevation" refers to the difference from a nominated reference surface (such as sea-level, or a mathematical/geodetic model that approximates the sea level known as the geoid). Elevation may be specified as normal height (above a reference ellipsoid), orthometric height, or dynamic height which have slightly different definitions.

St John's also has, on the south west face of it's tower, a Flush Bracket benchark with, possibly, a cut benchmark behind it [from the first leveling done by the OS].

liits wrote: St John's also has, on the south west face of it's tower, a Flush Bracket benchark with, possibly, a cut benchmark behind it [from the first leveling done by the OS]. Thanks liits for that information. I shall have a look for it the next time I'm the area.PS. There are some good astronomy photos in your Flickr section.

IIRC there's also one near to the side entrance of Holy Trinity Church too, about waist high.

We used to use datum marks which were pretty much similar to benchmarks, only you could find them on temporary bits of wood, or simple pencil marks. The engineer set them out inside buildings using the theodolite, and they were the set points to set all other fixtures and fittings to such as the height of suspended ceilings e.t.c. I'm old enough to remember using a water level while I was an apprentice joiner, a simple device but a really accurate way of transferring levels across a building, and even around corners. I'm really surprised to see you can still buy a water levelWhen I left the building trade the new technology was upon us, they were using laser levels, a rotating head that flashed a red beam around the buildinghttp://www.machinemart.co.uk/images/library/pr ... 0075.jpg?2        We thought they were truly amazing, but in those days many of the old hands were still using wheel braces, a cordless drill was a new and expensive luxury item, and not the necessity like it is now. Health & Safety as we know it today was non existent, all we had on the job was one clerk of works who worked independently for the client. Guys wearing a hard hat or safety boots were in the minority, and indeed if everyone wanted a hard hat they would nowhere near have enough, we pulled the lining out of them and used them to carry nails in. There was no tests or cards issued for any of the machinery or tools like there is today.             

Chrism wrote: IIRC there's also one near to the side entrance of Holy Trinity Church too, about waist high. Think I spotted one on Church wall junction Cookridge St/St Anne's St.According to Keith Waterhouse in his book 'City Lights' there was an air raid shelter in the Church yard too. Probs a temporary one soon 'filled'.

Leodian wrote: The photo shows a well defined bench mark (BM) a couple of blocks above the pavement. The wall is that at St John's church grounds facing New Briggate. A BM is marked there in an 1891 1:500 map in the excellent Old-Maps UK website (as also are the nearby steps). The BM does though looks too well defined to be that from at least 1891 and also the long block that part of the BM is on is not the same as virtually all of the other slabs the wall is built of. It seems likely therefore that this BM is not the original one. Hi Leodian. The fact that the bench mark appears across the join of two stones suggests to me that it was carved to an already existing elevation, and is therefore, as you say, not the original one. Perhaps the whole wall has been rebuilt since 1891? Or at least since the original measurement was taken.