Yes and no. I am apparently in the minority, but let me try once more to clarify the point I am making. First, if converting an actual measurement, it must ALWAYS be rounded sensibly at the end. There is no point in "decimal dust" in the final answer. Secondly, any rounding of the conversion factor can contribute to total rounding error. To minimize this, it should be accurate to at least one more figure than the number being converted, and it does not hurt if it is either exact or considerably more accurate than the number being converted. (If entering numbers by hand, you don't need to go overboard). Sometimes in intermediate calculations which will be used for further calculations, one guard digit is not sufficient and two or more should be considered. (certain quadratic solutions, trigonometry involving small cosines, etc, these are collectively known as "one minus one" problems). Finally,conversion factors are mostly declared or statutory numbers. 1 gallon = 231 in³ exactly, 1" = 25.4 mm exactly. so there is an exact value for converting a gallon or any submultiple to metric. The exact value need not be used, good enough is good enough. However, when an author whines, "I don't know if it is 236.6 mL, 238 mL or 240 mL," there IS an exact value, and a bunch of sensible approximations. (238 is plain wrong, to the stated precision) I don't seriously expect anyone to use 236.588 2365 mL/cup, but that happens to be the exact value, so there is an exact answer. Depending on purpose, 240 mL, 237 mL, 236.6 mL, 236.59 mL, etc may be suitable approximations. 240 mL may be a fine approximation for kitchen cooking. For net contents, if you actually measured out 1 cup, calling it 240 mL would be illegal as it overstates it, and the amount of overstatement would be a violation of Handbook 130. (For net contents, FTC mandates a conversion factor good to 6 digits for comparing metric and Customary statement) In a computer program, I would use the exact value above and a rounding routine that rounds the answer after parsing the input being converted. In a calculator, I would probably key in a 5 digit approximation as it exceeds any commercial weighing or measuring standards. To me, it is not worthwhile memorizing half a dozen conversion values dpending on the digits in the number being converted.
--- On Fri, 4/17/09, Jeremiah MacGregor <jeremiahmacgre...@rocketmail.com> wrote: From: Jeremiah MacGregor <jeremiahmacgre...@rocketmail.com> Subject: [USMA:44721] Re: Cooking using Cups To: "U.S. Metric Association" <usma@colostate.edu> Date: Friday, April 17, 2009, 10:39 PM It takes a bit of knowledge in numeracy, which is lacking in those who prefer imperial, to understand how to properly convert a dimension from inches to millimetres. For example, most would simply convert one inch as 25.4 mm. But if you take into account the tolerance of the dimension, you can round to a more sensible metric number. Most measurements in inches are not really that precise, even if someone may claim them to be. Fractional dimensions are the least precise, and from my experience may even vary a few millimetres either way in actual tolerance. Thus the calculator value is not always the best answer and rounding to the nearest millimetre often gives a better means to measure and produce in the future without problems of fit that some might expect if the calculator value is not adhered to. So, when converting one inch, the closest millimetre value to go to would be either 25 mm or 26 mm. If possible then 24 mm. 24 mm or 25 mm would be preferred over 25 mm as half dimensions of either still result in a whole number. 24 mm would be the best choice if possible as it can give you more whole numbers each time the dimension is halved before you encounter a decimal part. Of course it takes a little effort to come up with an acceptable value and like cooking from converted recipes, some amount of testing may be needed, but in the long run it is worth the effort when one can now work with a sensible number in whole millimetres. Jerry From: Pat Naughtin <pat.naugh...@metricationmatters.com> To: U.S. Metric Association <usma@colostate.edu> Sent: Thursday, April 16, 2009 3:46:49 PM Subject: [USMA:44704] Re: Cooking using Cups Dear John and All, It seems to me that it is a common trap for people new to metrication to get immediately involved in metric conversion where the first part of the process is to become amazed at the complexity of all of the old pre-metric measures and to try and describe them all, together with their faults. To my mind, this is a step in the wrong direction that makes some, but very little, progress toward metrication. But it is fascinating; and you can spend countless hours and days going down this path. See http://www.metricationmatters.com/metric_conversion.html for some thoughts on this pathway. For cooking, my wife and I have considered this issue carefully as we compiled several different cook books for local charities. Our approach was the direct metrication approach where we tool a role as metrication leaders. To do this we collected all of the special recipes from many wonderful old cooks from many parts of the world, converted their recipes to simple metric units using generally whole numbers, then test-cooked the lot of them — Yummm! See http://www.metricationmatters.com/docs/MetricCookingWithConfidence.pdf Notice that our readers, the grand children and great grandchildren of our recipe suppliers will never have to see the names of the old pre-metric measuring words in our cook books except for teaspoons, tablespoons, and cup, which we define wherever they are used. Our readers will never have to do any conversions from all of the old measuring methods to modern metric units; they can start to cook straight away using metric units only. Discussions about the different sizes of cups and spoons are possibly best left to academic historians while the rest of us just get on with our lives. Cheers, Pat Naughtin Geelong, Australia On 2009/04/17, at 12:54 AM, John M. Steele wrote: OK, he is frustrated, I get that. However, he goes out of his way to be confused by American volumetric measure issues which can be cleaned up by better research. A few points, commenting ONLY on American measure. *Measuring cups and spoons have well defined volumes, "common" cups and spoons (real expresso, tea and coffee cups, real flatware) don't. Use measuring cups and spoons to measure. *1 US gallon = 128 fl oz = 3.785 411 784 L, exactly. NIST Handbook 44, Appendix C defines the cup as 8 fl oz, the Tablespoon as 0.5 fl oz, and the teaspoon as 1/3 Tablespoon. These values are (rounded slightly) 236.5882 mL, 14.786 76 mL, 4.928 922 mL (from NIST SP811). *Rounded values of 240 mL, 15 mL, 5 mL are specified by law ONLY for serving sizes in the nutrition label (specified by FDA), and are NOT accurate enough for net contents labels (specified by FTC). They are probably "good enough" in the kitchen, but it should be understood they are rounded. Measuring Tablespoons are commonly marked 1 Tbsp / 15 mL; it is not clear whether they are really 15 mL or nearer 14.79 mL, but it probably doesn't matter in cooking. He is welcome to remain as confused as he wishes to be, but his questions have answers. It does seem that elsewhere, volumetric cooking measure is not as well defined, probably because they don't use it anymore. --- On Thu, 4/16/09, Michael Payne <metricm...@verizon.net> wrote: From: Michael Payne <metricm...@verizon.net> Subject: [USMA:44698] Cooking using Cups To: "U.S. Metric Association" <usma@colostate.edu> Date: Thursday, April 16, 2009, 9:35 AM http://www.lemis.com/grog/recipes/measures.php Interesting take on the various size of cups around the world as well as some units from Colonial Malaysia. Mike Payne Pat Naughtin PO Box 305 Belmont 3216, Geelong, Australia Phone: 61 3 5241 2008 Metric system consultant, writer, and speaker, Pat Naughtin, has helped thousands of people and hundreds of companies upgrade to the modern metric system smoothly, quickly, and so economically that they now save thousands each year when buying, processing, or selling for their businesses. Pat provides services and resources for many different trades, crafts, and professions for commercial, industrial and government metrication leaders in Asia, Europe, and in the USA. Pat's clients include the Australian Government, Google, NASA, NIST, and the metric associations of Canada, the UK, and the USA. See http://www.metricationmatters.com/ or to get the free 'Metrication matters' newsletter go to: http://www.metricationmatters.com/newsletter to subscribe.
