*Physician's Notebooks 2*- http://physiciansnotebook.blogspot.com - see*homepage***Reading the following section may increase your scores on tests - IQ, SAT, MCAT, TOEFL - and get you a free or very low cost education scholarship.**

__2.6g-1: Measurements in Science: Updated, 19 October 2018__

*Metric*– When the scientists got**together in Paris in 1791, first thing was to create a basic unit to replace the measures of the old, bad days; to create a measure of validity based on a natural value that could be checked objectively anytime – permanent, immovable, solid. So they decided to use the curvature of Earth as reference for the basic unit, and they named it "**

*m**eter"*

**after the French**

*metre,*

**itself deriving from Greek**

*metros*

**– measure. The meter relates to Earth’s meridian, a series of great circles that run along its global surface north-south through the poles and form longitudes on maps. Chief is the Prime Meridian, longitude 0**

^{0}

**that runs north-south through**

**Greenwich**

**England**

**. Surveyors, by making measurement along 2**

^{0}east longitude between Dunkirk and Barcelona, measured the surface distance of the meridian quadrant (1/4 of a meridian circumference of Earth) and took one ten millionth (1/10,000,000 or 0.0000001 or 10^{ –7}) of it and**created the meter. (It was not perfectly accurate but, practically, is very close.**

**For an American, a meter is 39.37 inches or 3 odd inches more than 3 feet. Knowing only feet or inches is only the knowledge of each number but if you know a meter all you need do is multiply by 10 and append 7 zeroes and you have 1/4 of the Earth’s transpolar circumference. Doing it in inches**

**39.37 x 10**

^{7}=3.937 x 10^{8}inches, and quick mental arithmetic gives Earth's circumference as circa 1.5 billion (1.5 x 10^{9}) inches, which**computes to 24,855 miles a value. Recent satellite assisted measurements of the transpolar circumference of the Earth give 24,901 miles. Wow! Isn't that a close confirmation of the Scientists of 1791?**

**The**

*liter*is the metric volume. You meet*liter*as word or suffix very much. Medical lab tests in fluids are reported per liter (or decimal of liter).**The liter is based on the meter. Without seeing a cube, I think everyone knows it is a box with 6 equal square panels of 6 equal sides. A liter is the capacity of a cube whose sides are 1/10 of a meter, or a decimeter (dm), so the formula for volume of cube (side x side x side) gives cubic decimeter for 1 liter. As with all metric units the liter is expressed in 10-unit groups; in the downward direction, eg, 1/10 liter = deciliter, 1/100 liter = centiliter, 1/1000 liter =**

*milliliter.*Stop here! “Milliliter" (ml) is the most frequently used unit of volume. Our bodies have 5,000 ml of fluid blood, or 5 liters.**The liter is 1.06 quart.**

**The cubic relation of meter to liter is seen in the common measurement unit**

*cubic centimeter*(cc) which is equal to milliliter (ml). How is this? Recall 1 liter = 1 cubic decimeter, or dm^{3}, and there are 10 cm in 1 dm so substituting we get 1 liter = (10 cm)^{3 }. Then 1 liter, which is 1000 milliliter = 1000 cm^{3}, so 1 ml = 1cc. Strictly, the “ml” should be preferred but “cc” is common.**In the**

**U.S.,**

**blood tests are reported in concentrations of grams (g) or milligrams (mg) per liter (l or L) or per deciliter (dL or dl).**

**An important household dose for fluids is teaspoon (5 ml) and tablespoon (15 ml).**

**The gram is used to measure weight. One thousand grams are 1 kilogram (kg) which weighs c.2.2 pounds avoirdupois (**

*libra,*or lb). One pound weighs c.455 grams or 0.455 kg.**A milligram of fluid since it has density near 1 gram per ml is about 1 ml. Thus 1 cc or ml of fluid weighs c.1 mg. Even solids can be roughly estimated this way, and since a teaspoon and a tablespoon is 5 ml and 15 ml, 1 flat teaspoon of sugar weighs slightly more than 5 mg, and 1 flat tablespoon, 15 mg. This is useful for home dosing when no other means of measure.**

**I should like to head off confusion in the conversion of grams to the common American and British fluid and weight measure “ounces” (oz). If you are working with a weight, like in powders, it is in the avoirdupois system which is 16 oz = 1 lb, and 1 oz = 28.375 g but if you are working with fluids, 1 fluid ounce = 1.04 avoirdupois ounce. And note the obsolete (**

**Troy**

**) system where 12 apothecary oz = 1 lb, or 1 apothecary oz = 37.833 g. With fluid measure, always use “fluid oz” or else confusion will be sparked.**

**Today in 2018, the meter, the gram and the liter as well as the seconds of time are defined by standard measures kept at Sevres France. That's the metric system.**

**END OF THE SECTION. To read on now, click**

**2.7 The Periodic Table of the Chemical Elements**

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