A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Gary LaPook
Date: 2010 Aug 25, 22:26 +0200
This is very, very close to the first definition of the meter of one-ten-millionth the distance from the equator to the north pole as measured my some Frenchmen during the time of the French revolution. Since there are 5400 NM spanning the same distance, using the first definition of the meter would make the NM 1851.851851851 meters making their measurement accurate to within 0.008 %, an amazing accomplishment in th 18th century.
Paul Niquette wrote:
With your permission and giving you full editorial rights, I would like to publish your explanation of the METAR report as an entry in…
…giving attribution to you as you might care to specify.
P.S. May I assume that you are having a wonderful trip in the
? Landof Gaulle
From: Gary LaPook [mailto:firstname.lastname@example.org]
Sent: Saturday, August 21, 2010 2:44 AM
To: NavList@fer3.com; Roger Ellis; solzman; Robert Deutsch; Linda Pendleton
Subject: Re: [NavList] Ah, give someone a calculator.......
As another example of what someone can do when handed a calculator, there are two stories out today headlined:
"The Moon Is Shrinking"
The stories report, that based on some cracks observed on the surface of the moon, that the crust has shrunk and that the moon has gotten about 100 meters smaller. And this involves a measurement made on an abject about 3,500,000 meters in diameter and about 385,000,000 meters away from earth.
But, give that 100 meter number (only one significant figure) to a guy and hand him a calculator and he converts it to 325 feet and, apparently a different guy, comes up with 328 feet!
(at least the second guy got the conversion right)
"Relative to the Moon's age, estimated at around 4.5 billion years, the contraction is recent, occurring less than a billion years ago, and is measured at about 100 metees (325 feet)."
"According to the study, there has been about 328 feet (100 meters) of change in the moon's radius over the course of about 1 billion years, said Watters. "
Gary LaPook wrote:
It's raining right now in
. I went online to the Weather Underground site to get a forecast at : Paris
According to Weather Underground:
Scattered Clouds 853 m
Few 1005 m
(Above Ground Level)"
How do you measure the base of clouds to the precision on just one meter? Isn't even the idea of a cloud something vaporous and indistinct?
Of course the answer is that you can't measure the base of clouds to such a level of precision, it is merely the work of someone with a calculator who can punch in numbers but who has conception of what the numbers actually mean.
The actual weather measured at Charles de Gaulle Airport is :
METAR LFPG 141200Z 08004KT 020V120 9999 SCT028 FEW033TCU 18/10 Q1016 NOSIG
This is the METAR format familiar to every pilot, and encodes the weather in a standard format.
METAR = regular hourly meteorological observation.
LFGP = code for Charles de Gaulle Airport,
141200Z= observation taken on the 14th day of the month at 1200Z.
08004KT 020V120 = wind is from 080° at 4 knots and the wind direction is variable from 020° to 120°.
9999 = visibility is at least 10 km.( 9999 meters)
SCT028 FEW033TCU = scattered clouds at 2800 feet and a few clouds at 3300 feet above ground level that are of the 'Towering Cumulus" type.
18/10 = temperature and dew point in degrees Celsius.
Q1016 = atmospheric pressure (altimeter setting) is 1016 mbar.
NOSIG = no significant weather.
The standard practice for measurring cloud heights worldwide is that they are measured to the nearest 100 feet as shown in the METAR, 2800 and 3300 foot clouds. Somebody then punched these numbers into his calculator and divided by the "feet to meters" conversion factor of 3.28084 which gets you to 853 meters and 1005 meters (mercifully they rounded to whole meters!)
Since the actual measurement was to the nearest 100 feet (meaning plus or minus 50 feet ) the lowest clouds could have been anywhere between 2750 and 2850 feet, 838 to 869 meters. A pilot reading 2800 feet understands the precision is to the nearest 100 feet but what is the obvious precision of 853 meters, plus or minus 1 meter? If someone had a brain who set up this conversion then he would have set it to give the heights to the nearest 30 meters which is consistent with the precision of the original data, say 860 meters and 1000 meters.