3 Comments for Can an handheld altimeter work inside a closed airconditioned car?

• 1. Joe  |  November 23rd, 2010 at 3:11 pm

  A closed, air-conditioned car isn’t truly airtight. Your barometric-pressure altimeter should work fine.

  It won’t work in a submarine, or a pressurized airliner, though.

• 2. Ecko  |  November 23rd, 2010 at 3:50 pm

  Depends on the accuracy you want. The car may be slightly pressurised, and that probably changes a bit with speed, but most cars are also open to the atmosphere so have to be quite close to the atmospheric pressure. An altimeter is normally accurate to somewhere between 10 and 100 feet, but 10 feet would need careful corrections. I doubt that the watch type is all that wonderful.

  I think you could easily verify the reading to your desired accuracy, and work out a way to open the windows so that the pressure is correct at least at some speed. Just use a stationary reading outside the car as a reference. Note that temperature difference, and the drift over time may be just as big a source of error. A barometer altimeter needs correction for the atmospheric pressure at the time, which is made by setting to read correct height at a known (reference) location.

  Another approach that is not affected by the wind or atmospheric pressure is a hand held GPS. The GPS system gives position in three dimensions, which includes altitude above the earth, using a reference plane. Look up geodetic to understand how to use it. You may need to make a geodetic setting that agrees with the reference of your maps depending where you live. The accuracy is not as good as the lat/long accuracy of a GPS, and is more “statistical” in nature than a barometric type. Expect 10-20m. You will have to decide what accuracy you want.

• 3. ?? Mr. Roach ??  |  November 23rd, 2010 at 4:22 pm

  If its the barometric type, there will be some errors in the reading. Probably insignificant since you are in a car and not flying.

  The ones that would be somewhat more accurate are the radio altimeters used in Air Force One/Two and many of the better aircraft that are Cat 1 landings.

  Ron

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