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View Diary: Measurement as a Way to Understand the World (121 comments)

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  •  Acre-foot is a very sensible unit (4+ / 0-)

    When you know you have 10 acres and you need 3 inches of water on them to keep your pasture growing. 2.5 acre-feet of water, please!

    For those not accustomed:
    An acre foot is enough water to cover an acre with 12 inches of rain.

    In my water district, which is northern California, pastures use, on average, 4.32 acre feet of irrigation water per acre per year, pears use 3.48, row crops use 3.57 and vineyards use 2.07 acre feet of water per acre per year. (These numbers include frost water.) These numbers do not include the water they naturally get from winter rains.

    Fry, don't be a hero! It's not covered by our health plan!

    by elfling on Tue May 28, 2013 at 12:24:50 AM PDT

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    •  And we are likely stuck with acre-feet (5+ / 0-)

      for a very long time. The underlying measurements for every piece of property in the US are the English units: feet for linear dimensions, and acres or square feet for the area measurements. All of the deeds and plats recorded in our courthouses are in these units. Changing to meters and hectares would be a monumental task.

      Canadians still refer to acres, even though their country has been metric for a long time.

      Probably the best we can do is to convert to acre-centimeters, or acre-meters.

    •  It's fine for its intended purpose... (2+ / 0-)
      Recommended by:
      RiveroftheWest, kyril

      My intended (but perhaps poorly made) point was conversions to and from that unit to more familiar units are likely to be known only to someone who does those conversions regularly.

      For many calculations, it's immanently reasonable. However, converting to or from gallons or cubic feet or cubic yards or liters or any more familiar unit is likely to be peculiar.

      A unit like a hectare-meter, conversely, would be straight-forward to convert to liters or cubic meters.

      •  I was just messing with you :-) (3+ / 0-)
        Recommended by:
        eyesoars, RiveroftheWest, kyril

        but it shows why a unit that seems completely peculiar remains in widespread use - because it's very convenient in real life.

        The ability to convert between cubic feet and acre-feet seamlessly is less important than the ability to specify the amount needed simply and accurately, in a way that makes error obvious. If I were to specify the water I needed in gallons or cubic meters, I could make an error by a factor of 10 and not catch it right away because it isn't intuitive. But no one is going to accidentally ask for 10 acre feet when they meant 1 acre foot.

        Fry, don't be a hero! It's not covered by our health plan!

        by elfling on Tue May 28, 2013 at 08:08:04 AM PDT

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    •  Sensible Unit?? (3+ / 0-)
      Recommended by:
      RiveroftheWest, BYw, kyril

      1/640 of a mile^2 * 12 inches
      43,560 ft^2 * 12 inches
      4046.8564224 m^2 * 0.3048 m

      I agree with foresterbob and others that it will be here for a long time, but it certainly is not sensible.

      The plural of anecdote is NOT data

      by Dr Arcadia on Tue May 28, 2013 at 04:42:06 PM PDT

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      •  That's because you're not irrigating acreage (3+ / 0-)

        It makes a lot of sense if you know your crop needs 12 inches of water a month during summer months and you're irrigating X acres. And that's exactly how people understand it and use it.

        1 acre foot times 20 acres: easy peasy.

        1233.5 cubic meters times 20 acres... um ... 24670 m3. Um, yeah. Intuitive. 25,000 cubic meters of water is much harder to visualize and understand, and if someone said, how about 20,000 m3, you don't have the same visceral understanding of what that will mean to your crop.

        The nice thing about acre-feet is how easily it converts in your mind to rainfall - large unit of land area times the amount of rainfall that fell on it, as an equivalent volume of water.

        I'm an engineer, and I'm comfortable and acquainted with metric, but it's worth appreciating that people use other units for real reasons, not just because Daddy Did.

        Fry, don't be a hero! It's not covered by our health plan!

        by elfling on Tue May 28, 2013 at 05:55:43 PM PDT

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    •  The acre is one of the earliest units of measure (2+ / 0-)
      Recommended by:
      elfling, eyesoars

      It starts out as the Mesopotamian iku, becomes an Egyptian 3kr, goes on to Greece as an are and Rome as an area. It didn't become 43,560 square feet till Queen Elizabeth 1 changed the length of the English mile from the old myle which was at 5000 foote the same length as the Roman miliare or the Greek Mia chilios.

      Anciently fields were planted in groups of two if plowed with an ox or three if plowed with a horse which allowed one to be left fallow.

      The Greek root stadios means 'to have standing'. Stadions are used to measure the sides of fields.

      In the time of Herodotus, the standard Attic stadion used for distance measure is 600 pous of 308.4 mm equal to 185 m. so that 600 stadia equal one degree and are combined at 8 to a mia chilioi or thousand which measures the boustredon or path of yoked oxen as a distance of a thousand orguia, taken as one orguia wide which defines an aroura or thousand of land and at 10 agros or chains equal to one nautical mile of 1850 m.

      Several centuries later, Marinus and Ptolemy used 500 stadia to a degree, but their stadia were composed of 600 Remen of 370 mm and measured 222 m, so the measuRement of the degree was the same.

      The same is also true for Eratosthenes, who used 700 stadia of 157.5 m or 300 Egyptian royal cubits to a degree, and for Aristotle, Posidonius, and Archimedes, whose stadia likewise measured the same degree.

      Live Free or Die --- Investigate, Incarcerate

      by rktect on Wed May 29, 2013 at 03:34:46 PM PDT

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