LSM9DS1 A 9 degree of freedom Inertial Navigation Chip

If you treat your stuff like code (with the three backticks) then you should be able to get it to appear a bit better (I changed it above).

I think it's just a typo, but you wrote atan2(y/z), when you need either atan(y/z) or atan2(y,z)

atan2 is clever, because 12/34 and -12 / -34 should be different angles, but obviously evaluate to the same number. atan2 checks and makes sure that it outputs a value that represents all 360 degrees, and not just 180.