Although I’m using a digital gyroscope, accelerometer and thermometer combined for SkySpy, in rummaging around on the internet looking at other accelerometers I found this fantastic guide on accelerometer calibration and orientation detection.  Although published by Analogue Devices for their ADXL335, everything is just as applicable for my choice – the InvenSense MPU-6050.  While non of it is rocket science, it’s great to find it written down by experts, rather than second-guess by noobs (me!).  Some of it even matches post-it notes and code I’ve spent many an hour thinking about!  My advice, save your brain power and use this version!