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The Ultimate Altimeter is a super-compact, Arduino controlled altimeter capable of measuring the altitude with an accuracy of 0.3 meters, and saving the highest and lowest values it has measured. It is powered by a 40 mAh Lithium Polymer battery, uses a tiny LCD Bubble Display, and measures altitude with a MPL3115A2 Altitude Sensor. It's very simple and fairly easy to build with just six major components. Additionally, an optional 3D printed case can house the Altimeter.
The Altimeter has a couple of different modes: current altitude, highest altitude, lowest altitude, difference in altitude (highest minus lowest), and standby (turns display off to save power for ~6 hr battery life, not shown in video).
The entire build adds up to around $30, but you may have some or most of the parts lying around already.
You can make this! It is not a very difficult project, and could be good practice for through-hole soldering, and coding (if you want to do modifications). Read on and create!