This is a nodejs module that is used to retrieve the data of GY-86 and connect 
it via respberry pi. Please run this on a raspberry. Need nodejs > 4.0.0. 
Please update your gcc/g++ on your raspberry to 4.8. Here is the instruction:
https://somewideopenspace.wordpress.com/2014/02/28/gcc-4-8-on-raspberry-pi-wheezy/

All of the APIs are synchronous. Synchronous APIs simplify the operation with
the device.

For calibration, only MPU6050 is supported. Be sure to place your GY-86 in 
horizontal position before you call the .calibrateMPU6050() function. Then 
a set of offsets is returned, including ax, ay, az, gz, gy and gz. You can
keep the offsets and call .setAccelXOffset(), .setAccelYOffset(), 
setAccelZOffset(), .setGryoXOffset(), .setGryoYOffset() and 
.setGryoZOffset() accordingly before .getMotion6() or .getMotion9() 
in your script. For HMC5883L, you can use python program in this page
http://blog.bitify.co.uk/2013/11/connecting-and-calibrating-hmc5883l.html
to do the calibration and use .setMagXOffset(), .setMagYOffset(),
.setMagZOffset() APIs to apply the offsets.

Datasheet:
MPU6050: https://www.olimex.com/Products/Modules/Sensors/MOD-MPU6050/resources/RM-MPU-60xxA_rev_4.pdf
HMC5883L: http://www51.honeywell.com/aero/common/documents/myaerospacecatalog-documents/Defense_Brochures-documents/HMC5883L_3-Axis_Digital_Compass_IC.pdf