Analog angle conversion from +70° to -70°
So atan2(y,x) gives the angle CCW from the x axis in radians, limited to [-pi,pi].  

If you want it converted to degrees CW from the Y axis, you would do 

azimuth=90.0-atan2(y,x)*57.295779;  


If you need to constrain it to -70,70 then:

azimuth_constrained=constrain(azimuth,-70,70);