Measuring using chains

[zwk500]

Not quite, as the circles of latitude shrink as you progress from the equator towards either pole! I would have said "(1/60 degree) of latitude at the equator" but Wikipedia (https://en.wikipedia.org/wiki/Nautical_mile) is more precise:

so a nautical mile is 1/60 of a degree of longitude or on the equator, or any other Great Circle.

In my defence, I was going off the introduction to that Wiki article:

Historically, it was defined as the meridian arc length corresponding to one minute (1/60 of a degree) of latitude. Today the international nautical mile is defined as exactly 1,852 metres (6,076 ft; 1.151 mi).

But I bow to your knowledge!

Mileposts on the Waterloo - Exeter line are a total mess. The difference between actual & milepost distances gradually increases all the way to Exeter, but not in any consistent pattern. Presumably different - and erroneous - surveyors chains were used during the original construction ??

Have no idea on this one, I'm afraid. I'd guess the individual contractors would be responsible for putting out the mileposts and their accuracy could be variable.

 

[AndrewE]

In my defence, I was going off the introduction to that Wiki article:

But I bow to your knowledge!

I don't know why they say that, as it is obvious that lines of latitude are shorter as you move away from the equator. At the poles it is just a few yards...
I remember which is which between lat. and long. by saying to myself that lines of longitude are all (equally) long.

 

[LNW-GW Joint]

Not quite, as the circles of latitude shrink as you progress from the equator towards either pole! I would have said "(1/60 degree) of latitude at the equator" but Wikipedia (https://en.wikipedia.org/wiki/Nautical_mile) is more precise:
so a nautical mile is 1/60 of a degree of longitude or on the equator, or any other Great Circle.

Hmm...
There are some differences with latitude as the earth is not a spheroid and bulges at the equator and flattens at the poles.
But broadly the nautical mile is 1/60 of a degree (1 arcmin) in latitude (ϕ) in a north-south direction.
With longitude, the same nautical mile will cover 1/60 / cos (ϕ) degrees in an east-west direction.
So at 60 north (cos (ϕ) = 0.5) the nautical mile will cover 1/30 degrees of longitude (ie 2 arcmin) in an east-west direction.

 

[MarkyT]

Interesting to note that 22yds is extremely close to 20m. It is actually 20.116840234m, but to get a rough idea of scale in metric, mutiplying a chain dimension by 20 is a good rule of thumb for mental arithmetic. There are modern metric surveyors chains available that are exactly 20m, and it was the original 22yd 'Gunters chain' (a convenient length able to be carried easily) used by early surveyors from where the unit derived.

 

[zwk500]

Interesting to note that 22yds is extremely close to 20m. It is actually 20.116840234m, but to get a rough idea of scale in metric, mutiplying a chain dimension by 20 is a good rule of thumb for mental arithmetic. There are modern metric surveyors chains available that are exactly 20m, and it was the original 22yd 'Gunters chain' (a convenient length able to be carried easily) used by early surveyors from where the unit derived.

The 1 chain = 20m is also part of the reason why it's survived in railway use, as a Mark 1/2 was 20m long, a Mark 3/4 23m long. So if you knew how many chains long a loop/siding/platform was, you knew how many vehicles could fit in it.

 

[snowball]

An early attempt to define the metre was as 1/10,000,000 of the distance from pole to equator measured along the meridian through Paris. If we adopted both this and the latitude definition of the nautical mile, it would be a logical, rather than geographical, fact that

90*60 nautical miles = 10000000 metres

or 1 nautical mile = 100000/54 metres = 1851.851851851... metres.

 

[MarkyT]

The 1 chain = 20m is also part of the reason why it's survived in railway use, as a Mark 1/2 was 20m long, a Mark 3/4 23m long. So if you knew how many chains long a loop/siding/platform was, you knew how many vehicles could fit in it.

And the Mk1s included most of the numerous Southern Region electric classes. Many of their later replacements currently in service have also continued the tradition with 20m cars.

 

[alxndr]

It’s been known by long serving track workers that many of these are somewhat out of position. In places where the chainage is still painted on the rails, it’s not uncommon for the chain mark to be different to the nearby post…

Or the numbers written to be nearly indecipherable, generally because they tend to be painted by someone leaning over the rail, so they're writing them upside down.

In a lot of areas where there has been no recent infrastructure investment, most records and documentation will be in miles & chains, or miles & yards. Sometimes in feet as well.

Or miles, quarter miles, and yards (e.g. 58 ¾ + 160).

Sounds like a nice yarn that the person in the pub spun for you.

I’ve seen absolutely no sign of any kilometre posts lineside or any references in any BR 1970s or later documentation. Parts of the Western Region have never even moved the mile posts, quarter, half and three quarter posts from the downside to the upside (normal practice is to have them on the up side, but on some lines, due to historical reasons they are on the downside) or replaced the non-Western type with Western types or the current style.

Agreed, I never saw any sign of this either.

Until the TVSC signalling scheme, I had never seen km used on the railway in my area. GWML ATP has however used metric metres for the distances and positions of the beacons and of the length of the infill loops. And the dimensions of various signalling equipment, allowable tolerances, specifications, checking gauges have been metric for many, many years.

Now all the TVSC signalling plans for my area all use metres for the distance and location measurements. Mile posts, quarter, half and three quarter posts are however still shown. Each has their location shown in metres below them. Like this:
View attachment 124377

Nearly everything else is in metric on these plans.

So, I often find myself converting between metres and imperial.

Plus the location cases themselves are named in miles and meters (e.g. MLN078U112 being at 78 mile and 1120 meters), which always frustrated me just because it feels wrong to combine metric and imperial in one measurement. Admittedly it does make converting to chain easy though, as you can approximate it accurately enough by assuming 20 meters = 1 chain.

IIRC Network Rail Scotland Route (alone?) uses miles and yards, not chains. Which made things interesting on the odd occasion measurements across the Route Boundary were required!

Also makes things interesting if you relocate and find everyone suddenly talking in yards, but your mind works in chain. The majority of people up here know that a chain exists, but rarely know how many yards are in a chain, or how many chain are in a mile. I find myself converting to chain to work anything out, because I can visualise those easily, and then having to convert back to yards to talk to anyone. Maybe I'll eventually get the hang of this yard business...

 

[R Martin]

When I was studying Electrical Engineering in the late 1950's I used Imperial Units, but by the time the 60's arrived we were all metric. Although I'm an old man now I don't have any problem with conversion between systems. The clue is to do all your calculations on the system provide and then convert the result to the system required. I have no problem with people using Imperial if they want to, I use both as required by the task in hand.

 

[Ken H]

When I was studying Electrical Engineering in the late 1950's I used Imperial Units, but by the time the 60's arrived we were all metric. Although I'm an old man now I don't have any problem with conversion between systems. The clue is to do all your calculations on the system provide and then convert the result to the system required. I have no problem with people using Imperial if they want to, I use both as required by the task in hand.

Quite. Dealing with old installations or historic buildings requires imperial units.
My windows are 5'2" wide. Its easy to measure. But you see tradesmen struggling to measure them in millimetres. They look at me blankly when tell them the measurement in imperial.

 

[Annetts key]

Plus the location cases themselves are named in miles and meters (e.g. MLN078U112 being at 78 mile and 1120 meters)

Which is why I decided not to mention these. Compared to the older Western method of identifying location cases, or location cupboards, or ‘locs’, where it was a letter followed by a number, for example B5, these are a bit of a mouthful. Especially near the start of a line such as “PAC000U007”…

And despite the current system being based on the distance, they are not always where they are supposed to be. The U for upside and the D for downside is mostly helpful, but not when the loc is in the middle/in between running lines…

Converting between imperial and metric or vice versa is fine as long as you use enough accuracy. Henry Williams ‘Domino’ panel tiles were imperial. The railway however ordered some replacements using metric measurements. When you have hundreds in a row, that soon shows up any conversation inaccuracy!

 

[plugwash]

The symbol "nm" properly means nanometres, but is sometimes improperly used for nautical miles, each of which is 1852000000000 nanometres.

The great thing about standards is there are so many of them to chose from.

 

[Ploughman]

Following the renewal of both Up and Down lines near Driffield back in 2008.
I was compiling the records for all the welds on the site.
These records applied to the lines individually and related to specified mileposts for each line located at stated Miles yds / chainages.
The specification was issued by NWR.
On completion the resulting welds were upto 50 yards different for welds directly opposite each other.
The matter of the different specified mileposts had been queried by me months previously but with no response other than carry on.
No one was bothered.

 

[alxndr]

Which is why I decided not to mention these. Compared to the older Western method of identifying location cases, or location cupboards, or ‘locs’, where it was a letter followed by a number, for example B5, these are a bit of a mouthful. Especially near the start of a line such as “PAC000U007”…

The new system does avoid instances such as ending up in Kintbury instead of Bedwyn, with the driver giving the excuse that they were "too busy going through 'S' locs in my head to notice where I was going."

And despite the current system being based on the distance, they are not always where they are supposed to be. The U for upside and the D for downside is mostly helpful, but not when the loc is in the middle/in between running lines…

I know of at least one which is on the wrong side for its identity, full stop. Spent quite a while hunting along the Up side before we discovered that for some reason it was installed on the Down.