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
