LMAO!!!!!
You know that at many truck stops they sell digital compasses that compensate for vehicle magnetics and are pretty accurate. I saw one selling for under $40 that operated from internal batteries or gigarette socket and even included inside and outside temperature sensors, elapsed timer and a photocell to automatically adjust the backlit display. I couldn't assemble one from scratch for that small price! That one will work with the vehicle shut off too when in battery mode!