1. You will NEVER get precise or accurate readings with a digital compass inside the basement of a house. You must test it in an area completely free from magnetic and electromagnetic interference. Caves work well! If you must be tethered to a laptop via USB for development, use a long 5-meter cable.
2. De-bounce your button press in firmware. Don't start sampling the sensor until you've delayed a small time interval due to the physical movement of the actuation. Even better, add a feature with a one or two second delay after button press like the delay on a digital camera; this is a feature that the DistoX sorely lacks.
3. Expect random variation from the sensor. Take multiple samples and combine them into an average. Consider throwing a "warning" if the distribution of samples is too wide, as this could indicate interference.
4. Do not be afraid to "stand on the shoulders of giants". See design docs for
DUSI,
DistoX,
Shetland Attack Pony.
5.
Lynn Brucker has a large amount of real-world digital instrument testing experience and has posted a great deal about it in the
Survey & Cartography forum.