const el = document.querySelector(`#el`); // My el with changing opacity


const args = {
    frequency:1000,                 //Tried with low and high frequency
    decimalCount:2
};


let gn = new GyroNorm();

gn.init(args).then(function(){
  gn.start(function(data){

    let opacity = data.dm.gx; // my opacity
    el.querySelector(`#fond`).style.opacity = opacity;

  });
}).catch(function(e){
  // log err
});

#el {
  transition: opacity 50ms;
}