By Brian Proffitt
Managing Editor
Altimeters… lie.
For those of you who are a bit uneasy about flying, this bit of
news may not make you feel any better. Nor will this piece of
information: most analog instruments on airplanes are prone to
quite a bit of error. Yet for over a hundred years, these
instruments were more than enough to get most aircraft safely from
place to place.
The reason for all of this non-accuracy is because the things
these instruments actually measure change as a plane moves from
place to place. Compasses are not 100 percent accurate, for
instance, because the magnetic north pole is not located at the
true north pole, so as a plane moves over long, cross-country
jaunts, pilots have to factor in degree variations to figure out
where north is.
Altimeters are even more finicky. Altitude is calculated on the
air pressure outside the plane. When you fly from one pressure
center into another, that change affects the measurement of the
instrument. That’s why most air traffic controllers regularly
update pilot in the sky with “altimeter readings,” which is really
just the air pressure at the airport measured in inches of mercury.
So, when I am flying into Indianapolis, and the flight controller
informs me the altimeter is “two-niner-niner-five,” I can dial my
altimeter to 29.95 inHg, and my altimeter will reflect a more
accurate altitude.
What makes this work is the constant flow of other information
that correct for all of the inherent errors in the instrumentation.
The radio lets me figure out what the pressure reading. My
transponder lets the air traffic controllers know where I am. My
map and the navigation radio can help me pinpoint my position and
my comm radio can let me ask the controllers (rather sheepishly)
where I am if I get completely lost. (Not yet, knock on wood.)
Now, in today’s more modern planes with glass cockpits of
all-digital instruments, such errors are non existent, or too small
to care about. I can turn on a GPS unit and see where I am
instantly, even in altitude. With newer navigation systems at
airports, such as the wide area augmentation system, GPS accuracy
is boosted to such a degree that with a WAAS-approved instrument
panel at an airport with a WAAS approach, I could (were I so rated)
a plane with very little visibility.
But in the event of an electrical failure, I would still have
standard-six cluster of analog instruments, just in case.
This sudden fixation on flying technicalities was actually
prompted by the story
yesterday about W3Counter.com’s revelation that the Linux
desktop has broken the two-percent mark in total deployment.
It seems such a small number, except when you take into account
that Macs, according to the same data, only comprise 5 percent of
the desktop market. Then things are put into a different
perspective.
But still, this survey, and all the others like it, are really
analogous to flying a plane with analog instruments. They each
individually may be very wrong, but when data is collaborated from
the other instruments, then a clearer picture can be formed.
I submit that these numbers do not give a true picture of the
state of the Linux desktop by themselves. But when put together
with all of the other clues, you can get a better sense of where
things are going: Windows is coming down; Mac and Linux are going
up. How fast and how much? Well, that’s still Magic 8 Ball
territory. Ask again later. It would be nice if there were
something analogous to GPS/WAAS for determining real desktop
numbers. Maybe something will be created soon to handle that. In
the meantime, we can take comfort in the fact that Linux is slowly
gaining altitude.
And as any pilot will tell you, the more space there is between
you and the ground, the better.