Damage to Chesterfield Canal, Worksop

[George and Dragon]

Time is based on a physical constant, the rotation of the earth (for the pedants out there I am aware that the speed of the earth's rotation is not constant). 

The metre was based on a physical constant, the length of the meridian that passes through Paris.

The kilogram was based on the weight of a fixed volume of water at a set temperature (I forget the details, it may have been a cubic decilitre, and I don't think I ever knew the temperature).

 

These are the three fundamental SI units, they have all been redefined as more accurate measuring methods became available.

I suspect you know all this already  .

[Athy]

5 minutes ago, Arthur Marshall said:

And fifty two weeks in a year? It's ridiculous.

From memory, Napoleon I & co. tried out decimal dates and time but it didn't really catch on.

[rusty69]

12 minutes ago, Athy said:

Ooh, you subversive fellow.

Why hasn't time gone metric yet?  These sixties and twenty-fours are so difficult to comprehend. I think we should be told.

It's obvious why time hasn't gone metric. If we only had 20 hours in a day, we never get anything done. If we had 30 hours in a day, we'd have far too much time on our hands,and have to spend even more time on Internet forums. 

[Alan de Enfield]

1 hour ago, Athy said:

Ooh, you subversive fellow.

Why hasn't time gone metric yet?  These sixties and twenty-fours are so difficult to comprehend. I think we should be told.

 

Compasses have gione metric with 400 degrees (ie 100 degrees between each of the cardinals).

 

I was teaching some Scouts Orienteering at an Intertional Jamboree when one group kept heading off in the wrong direction - it turned out they use the 'metric' compass in Norway, so when I gave them a heading of 270 degrees, instead of heading due West they headed off in error of half a Cardinal South West.

 

The 400 degree compass was originally introduced by the French, but apart from Norway, Sweden and Switzerland it is rarely seem now.

[Steve Buxton]

2.4 metres of 3" x 2" please.

 

[IanD]

3 hours ago, George and Dragon said:

I was going to suggest that speeds on inland waterways might be best expressed in metres per second (mostly to wind up Athy a little) but 4 mph is 1.78816 m/s which isn't a very user friendly number. However, as near as dammit, it's 2 yards per second. Actually 1.9555.

A much easier number to remember is that 4 mph is almost exactly 5 femto-light-fortnights-per-second... 😉

[Momac]

3 hours ago, Alan de Enfield said:

 

Compasses have gione metric with 400 degrees (ie 100 degrees between each of the cardinals).

 

I was teaching some Scouts Orienteering at an Intertional Jamboree when one group kept heading off in the wrong direction - it turned out they use the 'metric' compass in Norway, so when I gave them a heading of 270 degrees, instead of heading due West they headed off in error of half a Cardinal South West.

 

The 400 degree compass was originally introduced by the French, but apart from Norway, Sweden and Switzerland it is rarely seem now.

There is  such a thing but they are not called 'degrees'

https://en.wikipedia.org/wiki/Gradian

 

[George and Dragon]

8 hours ago, MartynG said:

There is  such a thing but they are not called 'degrees'

https://en.wikipedia.org/wiki/Gradian

 

I came across these at school. Never heard of them since. And now with the benefit of many years experience of the world I reckon they were a solution in search of a problem.

[Alan de Enfield]

8 hours ago, MartynG said:

There is  such a thing but they are not called 'degrees'

https://en.wikipedia.org/wiki/Gradian

 

 

Indeed but if I had said there are 100 grads in a right-angle and each grad can be subdivided into 100 centigrad some may not have understood.

 

The other measurement system used on a compass is the "Mils" and there are 6283 'mils' in the circle. These compasses have a wide use in the military and are used to give distance and size of an object (they are even engraved into the optics in military binoculars so you can estimate distance for range finding.

 

My Sniper compass with 'MiIls'. (6400 'units' shown in 100ths. ie 64 to the circle)

 

 

 

Another unit of measure, the radian, is used mainly by militaries in artillery, tank, and mortar gunnery.
There are 2 PI radians in a circle. PI is a constant of approximately 3.1416. That is 2 * 3.1416, or 6.283 radians. Divide each radian into 1000 mil-radians and you see there are 6283 mil-radians in a circle. Mil-radians are called mils for short.
17.78 mils equal 1 degree.

Compass use of mils typically rounds 6283 to 6400 for simplification. Some foreign militaries have simplified the other direction and divided the compass face into 6000 units, exactly like the face of a watch, with 100 units the same angle as a minute on the watch face.

Using mils, the actual size of an object observed in the field can be estimated. An object that appears to be n mils wide when it is 1000 units away from you, is actually n units wide - the units used does not matter, feet, yards, meters, miles
A vehicle that appears to be 15 mils long and is 1000 feet distant is actually 15 feet long. Or, two vehicles that appear to be 100 mils apart and are 1000 meters away, are actually 100 meters apart.
Conversely, if you know the size of an object, you can estimate its distance from you. If the tops of two mountains are 1 mile apart on your map, but they appear to be 100 mils apart, you must be 10 miles away.
Sighting on a man (approximately 6 feet tall) who appears to be 12 mils tall must be about 500 feet away. If he seemed 3 mils tall, he'd be 2000 feet away.

[George and Dragon]

6 minutes ago, Alan de Enfield said:

 

Indeed but if I had said there are 100 grads in a right-angle and each grad can be subdivided into 100 centigrad some may not have understood.

 

The other measurement system used on a compass is the "Mils" and there are 6283 'mils' in the circle. These compasses have a wide use in the military and are used to give distance and size of an object (they are even engraved into the optics in military binoculars so you can estimate distance for range finding.

 

My Sniper compass with 'MiIls'. (6400 'units' shown in 100ths. ie 64 to the circle)

 

 

 

Another unit of measure, the radian, is used mainly by militaries in artillery, tank, and mortar gunnery.
There are 2 PI radians in a circle. PI is a constant of approximately 3.1416. That is 2 * 3.1416, or 6.283 radians. Divide each radian into 1000 mil-radians and you see there are 6283 mil-radians in a circle. Mil-radians are called mils for short.
17.78 mils equal 1 degree.

Compass use of mils typically rounds 6283 to 6400 for simplification. Some foreign militaries have simplified the other direction and divided the compass face into 6000 units, exactly like the face of a watch, with 100 units the same angle as a minute on the watch face.

Using mils, the actual size of an object observed in the field can be estimated. An object that appears to be n mils wide when it is 1000 units away from you, is actually n units wide - the units used does not matter, feet, yards, meters, miles
A vehicle that appears to be 15 mils long and is 1000 feet distant is actually 15 feet long. Or, two vehicles that appear to be 100 mils apart and are 1000 meters away, are actually 100 meters apart.
Conversely, if you know the size of an object, you can estimate its distance from you. If the tops of two mountains are 1 mile apart on your map, but they appear to be 100 mils apart, you must be 10 miles away.
Sighting on a man (approximately 6 feet tall) who appears to be 12 mils tall must be about 500 feet away. If he seemed 3 mils tall, he'd be 2000 feet away.

 

Every day is a school day.

[rusty69]

15 minutes ago, Alan de Enfield said:

If the tops of two mountains are 1 mile apart on your map, but they appear to be 100 mils apart, you must be 10 miles away.

Sighting on a man (approximately 6 feet tall) who appears to be 12 mils tall must be about 500 feet away. If he seemed 3 mils tall, he'd be 2000 feet away.

If the tops of two mountains are 1 mile apart on your map,surely it's time to get a smaller map. 

Edited August 20, 2022 by rusty69

[David Mack]

11 hours ago, Alan de Enfield said:

Another unit of measure, the radian, is used mainly by militaries in artillery, tank, and mortar gunnery.

Really? The radian is surely more often used by mathematicians.

[Alan de Enfield]

2 minutes ago, David Mack said:

Really? The radian is surely more often used by mathematicians.

 

AS a compass it is mainly used by the military (rather than leisure users, shipping, aicraft etc)

[Mike Todd]

On 20/08/2022 at 10:23, Steve Buxton said:

2.4 metres of 3" x 2" please.

 

Planed or rough sawn?

 

Neither are actually 3 by 2.