The Boat Behind You.......

[alan_fincher]

Don't remeasure it today Dave or all your calculations will be up the Swanny with this sun!

 

George ex nb Alton retired

 

As long as his tape measure is made of similar steel to his boat, and has got equally hot, the readings may not change by much!

[furnessvale]

 

As long as his tape measure is made of similar steel to his boat, and has got equally hot, the readings may not change by much!

:-)

[Guest]

The trouble now, of course, is that we'll all be speculating as to why Linda posted Martin's comment twice but wrote nothing about it.

 

Clearly it was such a scintillating and magnificent contribution to the thread it was worthy of amplification.........twice.

[Mike Todd]

 

Not at all.

 

Accuracy is about the value being correct within the claimed margin of error.

 

Precision is about what the margin of error is.

 

If I tell you that my boat is 58' 0" long, that actually tells you that it is somewhere between 57' 11.5" and 58' 0.5"

 

It is an accurate measurement, to a precision of 1"

 

If I convert that to metric, and tell you that my boat is 17.6784 m long, I have told you something that is more precise (because it now says that the boat is between 17.67835m and 17.67845m, a precision of 0.01mm, or considerably better than a thou).

 

That value is VERY precise, much more than the original value, but possibly less accurate, as the true length may lie outside the implied range

Just so - although the actual example I had in mind was that the GPS unit may have a read-out that says the speed is 3.67 mph (a precision of 0.01 mph) but only have an accuracy (telling you what the real speed is) in the range 3.25 - 3.75 ie to the nearest 0.25 mph.

 

A popular confusion

[Athy]

 

Clearly it was such a scintillating and magnificent contribution to the thread it was worthy of amplification.........twice.

Since then, Linda has in fact posted in some detail - twice! What she had to say was interesting, and it also encouraged me to see that other people are as baffled by computer technology as I am!

 

Not at all.

 

Accuracy is about the value being correct within the claimed margin of error.

 

Precision is about what the margin of error is.

 

If I tell you that my boat is 58' 0" long, that actually tells you that it is somewhere between 57' 11.5" and 58' 0.5"

 

It is an accurate measurement, to a precision of 1"

 

If I convert that to metric, and tell you that my boat is 17.6784 m long, I have told you something that is more precise (because it now says that the boat is between 17.67835m and 17.67845m, a precision of 0.01mm, or considerably better than a thou).

 

That value is VERY precise, much more than the original value, but possibly less accurate, as the true length may lie outside the implied range

Hmmm.

David, I usually read your posts and they usually make a lot of sense.

This is perhaps the exception which proves the rule. A precise measurement is an accurate measurement and vice versa as far as I am concerned, though I will admit a difference in usage: we can say that a ruler is precisely 12" long, but we would not say that it is accurately 12" long..

[Guest]

Since then, Linda has in fact posted in some detail - twice! What she had to say was interesting, and it also encouraged me to see that other people are as baffled by computer technology as I am!

Hmmm.

David, I usually read your posts and they usually make a lot of sense.

This is perhaps the exception which proves the rule. A precise measurement is an accurate measurement and vice versa as far as I am concerned, though I will admit a difference in usage: we can say that a ruler is precisely 12" long, but we would not say that it is accurately 12" long..

 

If we are being totally precise we can actually only say a 12 inch ruler is precisely 12 inches long.

 

They come in other sizes

 

( more - actually there is usually a bit on either end anyway, making a 12 inch ruler a bit longer than 12 inches).

Edited July 19, 2016 by MJG

[Athy]

 

If we are being totally precise we can actually only say a 12 inch ruler is precisely 12 inches long.

 

They come in other sizes

 

( more - actually there is usually a bit on either end anyway, making a 12 inch ruler a bit longer than 12 inches).

Follicular bisection alert! Obviously only 12" rulers are 12" long, even I knew that. Oh, and those metal ones often don't have the headland, or whatever, which wooden ones have.

[cuthound]

Accuracy vs precision.

 

If you are shooting at a target and hit all shots close to the centre, but they spread about a bit (some above, some below, some to each side) your shooting is accurate.

 

If someone shoots and his shots are well away from the centre, but tightly grouped, they are precise.

 

Ideally you want both ☺

[zenataomm]

I am incredibly good looking in a classically handsome way, chiselled chin, piercing blue eyes, come to bed ears, masculine charged knees!

 

That is precise, yet is it accurate?

[RLWP]

I am incredibly good looking in a classically handsome way, chiselled chin, piercing blue eyes, come to bed ears, masculine charged knees!

 

That is precise, yet is it accurate?

 

Working from memory - not exactly...

 

Richard

[Captain Pegg]

David, I usually read your posts and they usually make a lot of sense.

This is perhaps the exception which proves the rule. A precise measurement is an accurate measurement and vice versa as far as I am concerned, though I will admit a difference in usage: we can say that a ruler is precisely 12" long, but we would not say that it is accurately 12" long..

The words are synonyms in terms of everyday usage. I understand where Dave is coming from although I am less than convinced by some of the other explanations.

 

A ruler may show precisely where 12" is on the scale but the graduations will have a level of tolerance in the manufacture of the ruler. Therefore it has a degree of accuracy. If it is a cheap ruler it may very well be precisely inaccurate.

 

JP

Edited July 19, 2016 by Captain Pegg

[Guest]

Follicular bisection alert! Obviously only 12" rulers are 12" long, even I knew that. Oh, and those metal ones often don't have the headland, or whatever, which wooden ones have.

Follicular bisection is a CWFD speciality.

[Chertsey]

I could go on further - I have a Volvo, and certainly may of those are driven by plonkers also.

.

Never!

[Chertsey]

The knack of following the channel seems to be almost a lost art these days and I'm sure accounts for many complaints about shallow canals. I've seldom had problems in many complained of areas and this in a boat drawing around 2' 8" under way. I once gave the tiller to someone who is involved with local " working " boats, they seemed only able to steer a parallel course to the towpath, regardless of where the boat wanted to go. Cutting corners is another modern practice. In the old days the deep water was around the outside of bends, sensibly, giving full length craft the best line. The motoring parallel continues in many threads.....folk speak of parking boats, not mooring them and driving rather than steering. Maybe it's just me.....

Dave

It's a brilliant feeling when you learn to trust the boat... After all, it knows the canal a lot better than I do.

[FadeToScarlet]

It's a brilliant feeling when you learn to trust the boat... After all, it knows the canal a lot better than I do.

It's a lot less tiring!

 

I'm out of practice, need to get back to the cut.

[Mike Todd]

Since then, Linda has in fact posted in some detail - twice! What she had to say was interesting, and it also encouraged me to see that other people are as baffled by computer technology as I am!

Hmmm.

David, I usually read your posts and they usually make a lot of sense.

This is perhaps the exception which proves the rule. A precise measurement is an accurate measurement and vice versa as far as I am concerned, though I will admit a difference in usage: we can say that a ruler is precisely 12" long, but we would not say that it is accurately 12" long..

Speaking as a (once) physicist by training and with quite a bit of engineering background, your conflation of the two concepts is a widespread problem and can lead to very considerable difficulties.

 

It also leads to problems in interpreting statistical or stochastic data, in particular whether two measurements represent a difference or not. To take an immediate issue, opinion polls. Media often highlight what are quite small changes in opinion ratings without citing the accuracy, although the numbers are given with spurious precision. In fact, in many cases, the error bar on both readings is such that they may well represent no change in opinion.

The words are synonyms in terms of everyday usage. I understand where Dave is coming from although I am less than convinced by some of the other explanations.

 

A ruler may show precisely where 12" is on the scale but the graduations will have a level of tolerance in the manufacture of the ruler. Therefore it has a degree of accuracy. If it is a cheap ruler it may very well be precisely inaccurate.

 

JP

I recognise the difference between popular usage and technical terms where the same words often mean different things. However, the point which gave rise to this part of the thread was a technical matter and the distinction is vital, especially if you wish to take action based on the correct or incorrect usage. To repeat, a precise reading of 3.456 mph is very unlikely to be accurate to the scale implied by the readout.

[MtB]

To a mathematician, 2" means the same size as 2.000".

 

To an engineer, 2" means a dimension of roughly 2", while 2.000" means a far more accurate dimension of somewhere between 1.9995" and 2.0005".

 

 

 

(Edit to get my orders of magnitude right!)

Edited July 20, 2016 by Mike the Boilerman

[monkeyhanger]

Different strokes for different folks. I disagree with almost everything you have said, but respect your right to say it.

Having read an awful lot of your posts over the years, I find that I agree with a great deal of your sentiments. However, this time, we disagree. I'm very interested to know exactly which parts of my statement you disagree ( and agree) with, and why. Most of what I wrote was a simple statement of fact. I wasn't aware that anything I wrote was contentious.

[Athy]

Having read an awful lot of your posts over the years, I find that I agree with a great deal of your sentiments. However, this time, we disagree. I'm very interested to know exactly which parts of my statement you disagree ( and agree) with, and why. Most of what I wrote was a simple statement of fact. I wasn't aware that anything I wrote was contentious.

Not contentious at all, my dear fellow, I'm not taking umbrage, just having fun. I think my use of the word "most" gives a clue as to the parts with which I don't agree. But I shall fail to lose sleep over the matter.

[MissMax]

Have you chaps decided what length 12 inches is yet?

[Victor Vectis]

254mm?

[Ray T]

Have you chaps decided what length 12 inches is yet?

 

Yes, 304.79999999999995 mm

 

http://www.convertunits.com/from/inches/to/mm

Edited July 20, 2016 by Ray T

[Athy]

254mm?

Nah, miles (?) out. That's about ten inches. From boyhood I have been able to visualise 18cm, 25cm and 30cm, as those are the metric equivalents of the three most common sizes of record.

[MtB]

Have you chaps decided what length 12 inches is yet?

 

 

12 inches is a foot.

 

I have one and I keep it in the yard.

[furnessvale]

 

Yes, 304.79999999999995 mm

 

http://www.convertunits.com/from/inches/to/mm

You'll have to be more precise than that....................or do I mean accurate?

 

George ex nb Alton retired