In 1983, a meter was redefined as the length of the path traveled by light in a vacuum during a time interval of 1 / 299,792,458ths of a second.
Don't you like that better than just "39 inches"?

* Notice ug. and mcg. are both micrograms or 1/1,000,000th of a gram,
whereas mg. is a milligram or 1/1,000th of a gram.

** International Units are used here in the context of a specific measurement unit of POTENCY, not weight. Certain vitamins are measured in these units, which are not to be confused with the entire Metric system of values which is also called the 'International System of Units' (SI).

The value on every row is 10 times the following row.

Notice the conversion between liters and cubic inch - the old GM car engine of the 60s, the 389 cu. in. V8, is really slightly less than 6.4 liters!

The water is distilled, at its maximum density, with the barometer at 30 in.
Water serves as a standard substance for defining units of measure, and it's readily available.

* av. = avoirdupois wt.

** Gasoline weight varies based on oxygen content, up to 3% in some mixtures. Ethanol usually has the highest content and is now called Unleaded Premium. Because of the oxygen content, gasoline can be compressed, unlike water.

And because gasoline weighs less than water, it floats on top! Any water in your car's fuel tank will settle to the bottom, where the fuel intake is located, so the water gets used first!

Gas and water don't mix, they separate, but even worse, Alcohol and water mix very well. So, consider the Ethanol-blended gasolines - the ones containing alcohol -- that alcohol will mix with the water and totally contaminate the entire mixture of gas, alcohol, and water!!

The speed of sound in air increases with temperature, about 1.1 ft./sec./F.
So, at lower altitudes, it is more difficult to 'break the sound barrier'.
The speed of sound in liquids and solids is not appreciably changed with temperature.

Also see Temperature Drop w/ Altitude Increase

Body Mass Index is a method of appoximating how overweight or underweight a person is. The rather simplistic approach is subject to errors, yet provides a method the average person can use, requiring no equipment beyond a ruler and bathscale.

First, determine your height, in inches, then your weight, in pounds.

Now multiply your height times itself (NOT times 2). So 5' 7" is 67 X 67 = 4489. Remember that figure.

Now take your weight and divide it by that previous figure.

Finally multiply by 703. The result is your BMI.

An example - a person weighing 150 lbs., standing 5' 7" tall:
5' 7" is 67", and 67 X 67 = 4489.
150, divide by 4489 = 0.033415 X 703 = 23.49 BMI.

There is a lot of controversy about the accuracy of the scale. Some think it should be adjusted upwards, others think it should be even more draconian.

The original formula, using metric measurements:
BMI = (weight in kilograms (kg.) / (height in meters) ^ 2)

Revised for English:
BMI = (weight in lbs. / (height in inches) ^ 2) X 703

Example: 5' 2" and 150 lbs. person
Height in inches = 62,
62 squared = (62 X 62 =) 3844
150 lbs / 3844 = 0.0390218
Multiply by 703 = 27.43 BMI.


Note - The formula to determine the weight for a given BMI is:

Weight = (BMI / 703) X (height in inches) ^ 2

A 5' 7" person is classed as healthy until they reach what weight?
'Healthy' BMI is up to 25.
So 25 / 703 X 4489 = 160 lbs.

E-King is the standard King or Eastern King (may be only 76" wide)
C-King is the California / Western King
Super Single is the 3/4 size
Twin XL is 1/2 King size

Some manufacturers are adding or subtracting inches from these standard sizes, BE SURE to choose a mattress made by a company that can at least use a ruler!! - Else your sheets won't fit correctly!

Air Beds (inflatable) are very seldom these exact sizes and vary widely.

Mattress thicknesses are about 7" (old) to 10" (new) to 16+" (pillowtop). Box spring thicknesses are typically 5.5" (old) and 7.5" (new).
Measure the length of your legs to see if you'll need a step to get in bed. For safety and convenience, one's mattress should not be higher than one's crotch.

A typical California King WaterBed holds about 270 Gallons of water, and weighs about 2300 lbs (a little more than a ton).

The general rules for Roman numerals are:

When a symbol precedes one having a greater value, it subtracts from the first, as: IV=4

When a symbol follows one of equal or greater value, it adds to the value of the first, as: II=2 and VI=6

When a symbol is between two of higher value, it subtracts from the third, as: CIX = 109

When a symbol is repeated, its value is also repeated, as: XX=20, CC=200, CCC=300, LXXX or XXC=80

When a symbol has a horizontal line above it, its value is multiplied by itself or squared.

MCMXLIV = 1944, MCMLXXXII = 1982, MXMII = 1992 or MCMLXLII = 1992 or MCMLXXXXII = 1992, and MMIII = 2003
(Notice the first form of 1992 is correct, yet the second is used most often and sometimes the third.)

Why do many clocks and watches use 'IIII' instead of 'IV'?
I dunno. It may be for symetrical balance or because some Romans used 'IIII' before their kids starting using 'IV'.
Big Ben in England uses 'IV'.

Did you see any '0' (zeros) in those Roman Numerals?

In the strictest sense, decibels are only a ratio of two values. If a unit puts out 100 watts and another unit puts out 10,000 watts, then the ratio is 10000 / 100 or 100. On the Power ratio scale, a 100X difference = 20 dB, where the dB value is the 'log base 10 of the ratio'. For a voltage ratio, where it is 'log base 20 of the ratio', a 100X difference = 40 dB.

If you have 200 watts/100 watts = 2 X, or 3 dB, that is, a doubling of the power increases 3 dB. For each 10X increase in power, dB increases +10.

You may remember hearing of a decibel rating, or loudness, of jet engines. That may seem to be an absolute value, but is still just a ratio to a fixed reference.

For sounds, a '120 dB jet engine' refers to ratio of the loudness of the engine to a reference of 10 ^ -16   watts / cm sq., the faintest sound an average person can hear - or 1/1000000000000000th watt per sq. cm.

Electronically, a loudness level of 30 dB is really 30 dBm, or 30 dB above a '1 milliwatt across 600 ohms' reference.

120 dB is a more convenient value to use than saying '1,000,000,000,000 times louder than the softest sound you can hear'. Don't you agree?

Daylight Savings Date Changes
Starting in 2007:
Daylight Savings begins on the second Sunday in March at 2:00AM.
        Set clocks ahead one hour. (SPRING forward)

Daylight Savings ends on the first Sunday in November at 2:00AM.
        Set clocks back one hour. (FALL back)

(Prior to 2007, the change was on the first Sunday in April and last in October, which was 4 weeks less of Daylight Savings than now.)

Other Date Trivia
How is the date for Easter determined?
It changes from year to year. As decreed by the first Council of Nicea in A.D. 325, Easter is observed on the Sunday after the first full moon, on or after the vernal equinox, a range of 35 days. It cannot be before March 22 or after April 25.

What is the Julian Date?
Used by astronomers, it arbitrarily sets Jan 1, 4713 B.C. as the 0 reference. So Mar 16, 1997 is 2440523.5 Julian. The Julian day starts at noon, we start at midnight, hence the 0.5 on the end.

There was no year '0000'. The year 1 A.D. immediately followed the year 1 B.C.

What is the Julian Day?
The sequentially number day of the year, starting with 1 for Jan 1st, and ending with 365 or 366. Some calendars show both the Julian Day and the inverse - the number of days until the END of the year. Used for calculating the 'days between dates'.

When was the current Gregorian Calendar started?
It was the day after Thursday Oct 4, 1582, which happened to become Friday Oct 15, 1582! The 10 day 'adjustment' was necessary to get back in step with the sun - landlords loved it, renters hated that change, creating a 21 day month for October, 1582!

BUT that was only for Catholic countries following Pope Gregory XIII. England didn't change until Sept 2, 1752 and jumped to Sept 14, 1752. By then the error had increased to 11 days!!

Leap Years occur every 4 years (in years evenly divisible by 4), where one extra day is added to February, making it 29 days long. Exactly every 100 years (in years evenly divisible by 100), it should be a Leap Year, but they SKIP the extra day in those years. EXCEPT every 400 years (like 2000), where they ADD the SKIPPED Leap Year day back -- as they did in our year 2000.

Passing Time
The Atomic Clock allows the measurement of time and frequency to an accuracy much greater than any other physical quantity.

Note: GMT starts at noon while UTC starts at midnight.

By international agreement, UTC is kept within 0.7 seconds of UT1, by adding and subtracting 'leap seconds' from time to time.

The abbreviation of 'Coordinated Universal Time' is indeed, UTC.

All GMT and UTC derived times are in the 24HR format, 00:00 to 23:59.

The terms 'AM' and 'PM' are abbreviations for Ante-Meridian, meaning 'before the sun reaches the meridian or directly overhead', and Post-Meridian, 'after the sun reaches the meridian'.

In 1928, Greenwich Mean Time (GMT) was changed to Universal Time.

Before 1956, a second was defined as 1/86,400 of the mean solar day.

Then from 1956 to 1967, it was the ephemeris second, defined as 1 / 31556925.9747 of the tropical year at 00h 00m 00s 31 December 1899.

Currently the second is defined as 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium-133 atom.


TIME REVERSAL INVARIANCE is a type of reversibility that states if time could run backwards, where reversing time corresponds to reversing velocities, and collisions of idealized billiard balls would retrace their paths.

The letter designations actually circumvent the globe. All letters are used except "J". Do your math. There are 24 hours in a day, 24 time zones around the globe and 26 letters - 1 = 25. Why do we need 25 letters to name 24 zones?

First, Zulu is the zone centered on the Prime Meridian, 0° longitude, Greenwich, England. Each time zone is 15° (360° / 24 hours = 15°). So the Zulu time zone extends 7.5° of longitude east and west from the Prime Meridian. The center of the next time zone east of Zulu is 15°E longitude and is designated A or 'Alpha'. There are 12 time zones going east from Zulu - Alpha to Mike, covering Europe, Russia, China, and the Pacific Basin to the International Date Line.

Going WEST from Zulu in England, begins with November, and on to Romeo (for the Eastern time zone in the U.S.), to Uniform (Pacific time), and ends with Yankee at the International Date Line, which is -12 hours from Zulu.

Here we have the descrepancy, Zulu is a time zone, and +12 zones eastward brings us to Mike which covers the International Date Line. But going west from Zulu, we ALSO have -12 zones bringing us to Yankee which covers the International Date Line. That totals 12 zones one direction, 12 the other, and with one to start = 25 zones, and we know we only have room for 24!

Would it be correct to say, that the one zone over the International Date Line is really divided into halves? Perhaps Mike and Yankee are only half-sized zones?

The real answer is: in the single zone named both Mike and Yankee, it is always the exact same time (12 hours offset from Zulu), but it is never the same date!   Each side of the International Date Line is a different day, and the designation of Mike or Yankee for that same time zone indicates which is the correct date, within that zone.


And what ever happened to J, the time zone Juliet? That designation is reserved for the local time zone of the observer. If the correct time for the Pacific Time Zone (Uniform) is 9:00 AM, and you are there, then Juliet time, for YOU, is 0900.

OK, if I'm in Atlanta, near the 34th degree of Latitude, how far apart are the Longitude lines around here?

You'll need a scientific calculator, either hand-held, app-held, or website, with a Cosine function. And WATCH, we're going to do some astrophysical calculations!!!

Enter your Latitude, in this case "34", press the Cosine key/button/icon, and you'll see "0.829...". Press the multiply key/button/icon, and enter "69.11" and you'll see "57.294..."

You're done. Longitude lines crossing 34° Latitude are 57.294 miles apart. And, Latitude lines are 69.11 miles apart.

How does this relate to GPS values?

Most GPS devices can display your position in at least two formats:
Decimal Degrees (34.03917° - usually with 5-6 digits after the decimal)
or
Deg / Min / Sec (34° 02' 21")

When these numbers change by one digit, HOW FAR would that be on the Earth?

---

If you move North or South (Latitude change), each degree is 69.11 miles.

So 69.11 miles multiplied by 5280 feet = 364900.8 feet. If the Latitude changes from "34.03917" to "34.03918", that was a .00001 change or 1/100,000. Simply take the 364900.8 feet between Latitude lines and divide by 100,000 = 3.64. That's 3.64 feet for every digit change.

If the decimal degrees had 6 digits, then you'd divide by 1,000,000 and arrive at 0.364 feet or 4.368 inches...
For Deg/Min/Sec values, there are 60 minutes in a degree and 60 seconds in a minute, or 3600 seconds in a degree. We know 364900.8 feet per Latitude degree, so divide it now by 3600 = 101.36. That's 101.36 feet for each digit change in seconds.

So, the Decimal Degree format is more accurate? Yes and No -- Yes, it COULD be, NO it's NOT necessarily.

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Consumer GPS units are designed for 3 meter accuracy or better, which is almost 10 feet. Some MAY be more accurate. It depends on how many satellites it can lock onto, the signal levels, and the instrument.

Consumer GPS units aren't very repeatable. That is, take a reading HERE, walk over THERE, then come back HERE, and the reading probably won't be the same.

The least digit in the Decimal format is 3.6 feet but the GPS resolution is 3 meters, nearly 3 times that.

The Deg / Min / Sec format can display about a 100 foot change, which is 10 times more coarse than the 3 meter GPS accuracy, so that figure will change less.