Dear Rod I am glad you've diverted from the "accurate" vs. "precise" issue. You know, to me this is so confusing I though I could help myself bringing the terms into Portuguese. You know what? Things only got worse.
I was completely uncapable of presenting my own comments about the issue. Especially because in my speech I've never cared with the possible distinction between these two terms. But now that you referred to these Imperial measurement units I can confortably say: why don't you Anglophones try the metric system? It is so easy to handle that even some one that can not argue about the difference between "accurate" and "precise" can use it with accuracy and precision. :-) - fernando "A.R. EDEN" wrote: > Tom, > > As an old "old timer" I cannot resist the temptation, with tongue firmly in > cheek, to take you up on the meaurement of the diameter of a rod. Whether > it is accurate or precise, I do not know, but to me a rod is a lineal > measurement, and does not have a diameter. > > 72 points = 1 inch > 3 barleycorns (in length) = 1 inch > 12 lines = 1 inch > 12 inches = 1 foot > 3 feet = 1 yard > 6 feet = 1 fathom > > *** 5 1/2 yards = 1 rod, (pole or perch). *** > > 40 poles 1 furlong > 8 furlongs = 1 mile > 3 miles = 1 league. > > Square poles were used in my working lifetime for the measurement of > small plots of land (typically allotment gardens), but I expect they are all > in this new metric system. Very confusing. As no doubt you know :- > > 1 sq. pole = 30 1/4 sq. yds. > 40 sq. poles = 1 rood > 4 roods = 1 acre. > etc., etc.. > > I have never come across lines and barleycorns, but I came across a > reference to them some years ago which claimed that the last time lines had > been used as a standard measurement was was in an Air Ministry specification > for the size of the brass buttons on Royal Air Force uniforms, and that a > barleycorn, a third of an inch, still ingers on - tho' not perhaps by name > now - as the measure still used in boots and shoes. The difference > between a size ten and a size ten and a half shoe, it was said, is NOT half > the difference in size betweena a 10 and a 11, but is a size 10 plus a > barleycorn - a third of an inch! > > Apologies for any momentary distraction from more essential items, such > as sundials. > > Rod Eden > > ----- Original Message ----- > From: Tom Semadeni <[EMAIL PROTECTED]> > To: Phil Pappas <[EMAIL PROTECTED]> > Cc: <sundial@rrz.uni-koeln.de> > Sent: 29 April 1999 20:12 > Subject: Re: "accurate" vs. "precise" > > > Yo John! > > Old Timers?! > > Elderly?.....or on old time?.... or been on the list for a while?....or? > > > > My distant history tells me this: > > > > Precision usually means the number of significant figures used to report a > > measurement. > > Accuracy usually means how close your reported measurement is to the > "truth". > > > > Try this scenario: > > > > Let's say that the diameter of a rod is measured, using accurate laser > > interferometry, to be 0. 50148 cm. > > > > You measure the diameter with a micrometer using its vernier scale and > report the > > diameter (A) as 0.5025 cm . > > You then use a coarse pair of calipers and report its diameter (B) to be > 0.5 cm. > > > > Measurement A is MORE PRECISE because it implies a preciseness of > measurement > > 1000 times, or 3 orders of magnitude, more precise than Measurement B. > > > > But measurement A implies that the "true" value of the diameter is between > 0. > > 50245 and 0.50255 cm while measurement B implies that the "true" value of > the > > diameter is between 0.45 cm and 0.55 cm. > > So measurement B is MORE ACCURATE since the "true" value lies within the > implied > > limits of the B measurement and outside of the A measurement limits. > > (There is a systematic error in the A measurement of about 0.001 cm, > probably due > > to a non-zeroed anvil measurement.) > > > > > > Dial accuracy is affected by the accuracy of placement and orientation of > all of > > the components. > > Dial precision is affected by the clever use of geometry, scaling, and > > interpolation lines to aid the eye to read the edge or body of a shadow > > precisely. > > > > John Shepherd's beautiful dial at: > > http://www.uwrf.edu/sundial/welcome.html > > demonstrates a clever trick to increase the precision of an accurate dial. > The > > trick is shown explicitly at: > > http://www.uwrf.edu/sundial/images.html > > where the good Professor shows three close-ups taken sequentially at 9:58, > 10:00 > > and 10:02 am Central Daylight Time. > > The eye/mind is very good at extrapolating to a point, much better than > finding > > and reporting the edge of a fuzzy shadow! > > > > The short and long of it, John, is that you shouldn't use "accurate", > "precise" > > and "old timer" without proper explanation! > > > > It seems that there was a discussion on this list a long time ago about > tricks to > > help the eye get increased precision of dial time. There must be some > rules of > > thumb about shadow distance, contrast, color etc. that would help us in > our quest > > for precision (assuming that our dial is free of the normal errors!). I, > for > > one, would appreciate some pointers (pun) on the topic of enhancing > precision. > > > > Cheers, and congratulations at being at the proofreading stage of your > Manual. > > Good stuff. > > t > > > > Phil Pappas wrote: > > > > > Hello Old Timers: > > > > > > I've got another knit-picky question for you all to ponder. But you're a > > > rather knit-picky group, so I don't think you'll mind. > > > > > > In proofreading the new fifth edition of my "Sundial Owner's Manual", > when > > > discussing sundials, I think that I mistakenly used the words, "precise" > and > > > "accurate", interchangeably, as if they meant the same thing. > > > > > > > > > John Carmichael > > > Tucson > > > tel: 520-696-1709 > > > website: http://www.azstarnet.com/~pappas > > > > -- > > Tom Semadeni O > > [EMAIL PROTECTED] o > > aka I (Ned) Ames . > > Britthome Bounty ><<((((*> > > Box 176 Britt ON P0G 1A0 > > 'Phone 705 383 0195 fax 2920 > > 45.768* North 80.600* West > > > > -- Fernando Cabral Padrao iX Sistemas Abertos mailto:[EMAIL PROTECTED] http://www.pix.com.br mailto:[EMAIL PROTECTED] Fone: +55 61 321-2433 Fax: +55 61 225-3082 15º 45' 04.9" S 47º 49' 58.6" W 19º 37' 57.0" S 45º 17' 13.6" W
