70's wiring in new sockets

Or is the discussion actually about the accuracy of 22/7 Vs 3.14.............?
No, just how it came about - I think.

As you say "then discovering that represented 22/7". How did they determine that?
Surely they would have discovered that it was three and a bit times the diameter, and that bit was about a seventh of the diameter.
Only then would they realise the existence or relevance of 22.

I know it's being picky but I know what I mean.
 
Sponsored Links
... so the 22/7 approximation for pi works with any number of strands (or any other application that requires pi), whereas your way of looking at it only 'works' in the special case of 7-strand cable (and that because a "7" appears, co-incidentally, in the approximation to pi).

Kind Regards, John
Yes but I remember the figure because I've calculated the area of 7 stranded things so many times and in reality I'm more likely to do 0.6D² if it's in my head and accuracy isnt critical.
 
No, just how it came about - I think.

As you say "then discovering that represented 22/7". How did they determine that?
Surely they would have discovered that it was three and a bit times the diameter, and that bit was about a seventh of the diameter.
Only then would they realise the existence or relevance of 22.

I know it's being picky but I know what I mean.
Probably something a simple as 22 fingers width one way and 7 the other.
 
All I am saying is that anyone using 22/7 would not have come to that fraction by dividing 22 by 7.
As I said, it was the mere coincidence that we were talking about 7-stranded conductors that enabled you to 'look at it' the way you did.

The 22/7 "very good approximation to pi" has been known for centuries.

When I was at school and uni, if we wanted to do a 'manual (pencil and paper, or 'mental arithmetic') calculation' involving pi, then, unless we wanted an incredibly accurate answer (which we rarely did), we always used 22/7 (i.e. "multiply by 22 and then divide by 7") - and that was decades before I had any knowledge about, or interest in conductor, CSAs or stranded conductors of any size, let alone 7-stranded ones.

Kind Regards, John
 
Sponsored Links
Or is the discussion actually about the accuracy of 22/7 Vs 3.14.............?
It all started because, 'in passing', I innocently pointed out that 22/7 was extremely close to the value of pi - but I'm coming to regret that I did!

Kind Regards, John
 
No, just how it came about - I think.
It "came about" long before anyone knew what an electrical conductor (let alone a stranded one) was :) The 22/7 approximation for pi has been used for many centuries (actually millennia).

Around 250 BC, Archimedes established that 22/7 was an 'upper bound' for the true value of pi, by producing a mathematical proof (by considering regular polygons of ever-increasing number of sides) that the true value of pi was between 223/71 and 22/7. After that, the simple approximation (22/7) was used for centuries ... so, that a very close approximation (suitable for 'manual calculations') was 22/7 has been known for over 2,000 years.

Kind Regards, John
 
It all started because, 'in passing', I innocently pointed out that 22/7 was extremely close to the value of pi - but I'm coming to regret that I did!

Kind Regards, John
:unsure:I:rolleyes:know:(what:confused:you:cautious:mean(y)
 
It "came about" long before anyone knew what an electrical conductor (let alone a stranded one) was :) The 22/7 approximation for pi has been used for many centuries (actually millennia).

Around 250 BC, Archimedes established that 22/7 was an 'upper bound' for the true value of pi, by producing a mathematical proof (by considering regular polygons of ever-increasing number of sides) that the true value of pi was between 223/71 and 22/7. After that, the simple approximation (22/7) was used for centuries ... so, that a very close approximation (suitable for 'manual calculations') was 22/7 has been known for over 2,000 years.

Kind Regards, John
I'm surprised that 2250 years ago they had the measuring/construction accuracy to enable those figures
 
I'm surprised that 2250 years ago they had the measuring/construction accuracy to enable those figures
Well, I've just had a peep at the Wikipedia (which, fortunately, confirms what I remembered about Archimedes :) ) and there is even a suggestion (albeit 'regarded with scepticism' by some!) that the Ancient Egyptians used "22/7" in 2560 BC - which, if true, would be getting on for 5,000 years ago!

Kind Regards, John
 
...pi is actually 3.1415925.....
pi is actually 3.14159265...
I'm going to have to ask you to make some allowances for the sometimes imperfect memory of my ageing brain :)

Mind you, there is a (much younger) member of my family who can recite pi to at least a couple of hundred decimal places (I can't remember exactly how many) - but, for that (amongst other) reasons, I regard her as "abnormal" :)

Kind Regareds, John
 
i used to use 355/113 for PI to 6dp. But I memorised 3.141592654 years ago.
35500001/11300001 is good for 7dp.
 
I'm going to have to ask you to make some allowances for the sometimes imperfect memory of my ageing brain :)

Mind you, there is a (much younger) member of my family who can recite pi to at least a couple of hundred decimal places (I can't remember exactly how many) - but, for that (amongst other) reasons, I regard her as "abnormal" :)

Kind Regareds, John
Sorry. It just jars on me when I see people get it wrong! I only learned it to 50 places when I was at school. The reason was, I'd copied it out of a library book to 200 places, but at around digit 50 I couldn't read my own hand-writing so I had to stop there.
 
Sorry. It just jars on me when I see people get it wrong! I only learned it to 50 places when I was at school. The reason was, I'd copied it out of a library book to 200 places, but at around digit 50 I couldn't read my own hand-writing so I had to stop there.

3.1415926535897932384626433832795028841971
6939937510582097494459230781640628620899
8628034825342117067982148086513282306647
0938446095505822317253594081284811174502
8410270193852110555964462294895493038196
 

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.


Are you a trade or supplier? You can create your listing free at DIYnot Local

 
Sponsored Links
Back
Top