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How to Make Your Own Altimeter Barometric Parallax

An altimeter is a barometer that is used to indicate changes in height. A barometric altimeter uses changes in barometric pressure to calculate altitude. It uses the barometric pressure at sea level as a base measurement. Changes in atmospheric pressure cause liquid or mercury in the barometer to move up and down the mechanism. The height differences in the liquid/metal (Hg) are directly related to the changes in pressure at different altitudes, allowing you to calculate the height above sea level. Barometric altimeters are used in aviation to determine altitude during flight. Parallax manufactures sensor modules for use in aviation-quality barometric altimeters. You can make your own non-aviation-quality barometric altimeter using simple materials found around the house.

Things You'll Need

Plastic bottle
Clear plastic tubing
Water
Food coloring
Index cards
Sealant
Ruler
Pen
Tape

Instructions

- 1
  Cut the top off the bottle, if the opening is not wide enough to comfortably accommodate both the ruler and the clear plastic tubing.
- 2
  Place the ruler into the bottle, with the lower measurements starting at the bottom of the bottom and the higher measurements ending at the top. Secure the ruler in place with tape or sealant. You need to ensure that the ruler stays upright and straight, as you will be using it to measure the changes in water level. The entire ruler does not have to fit inside the bottle, as the top of the bottle is cut off.
- 3
  Secure the clear plastic tubing to the side of the bottle. It should be a few centimeters off the bottom of the bottle, i.e., not touching the bottom. You should place it as close to the ruler as possible, to allow for easy reading of the changes in water levels. Ideally, you should place it vertically flush with the ruler to be able to read the measurements.
- 4
  Pour water into the bottle until it is half full.
- 5
  Add a few drops of food coloring to the water. Use sufficient food coloring to give a distinctive color to the water, as this will make it easier to see the changes in water level and take measurements.
- 6
  Suck water into the tube until it is half-full. Use your finger to cover the top of the tube, keeping the water trapped in the tube at the half-way mark. Use sealant to permanently seal the top of the tube. The sealed end of the tube can be outside the cut end of the bottle.
- 7
  Mark the water level in the bottle. You can attach an index card to the outside of the bottle with tape to make the marking easier. Ideally, you should mark the base height of the water at sea level.
- 8
  Mark the changes in the water level with changes in height. You can then use the change in water level to calculate the altitude. The formula for calculating altitude (with mercury) is:
  Altitude indicated = ( 1,000 feet/in Hg ) x (Kollsman -- Actual Barometric )

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