ADC Noise

You can use a moving average with an interval of 8 or 16 samples .
I used the following code to get stable readings from a 10-bit encoder.
Using the dithered noise resolution is in fact improved to 1 1bits.

setInterval(function() {
        enc_deg = sma16(degree(C1).toFixed(1)); // console.log("Encoder Angle[°] = "+enc_deg.toFixed(1)); 
    }, 100 );
function degree( pin ) {
  var ratio  = 4.0;                  
  var offset = 0.5;       
  var factor = 0.73333333333; 
  var phys   = analogRead(pin) * 3.3;  // *E.getAnalogVRef(); 
  var meas   = 360.0 * ( phys / factor - offset ) / ratio ;    
  console.log("Input[V] = "+phys.toFixed(3)+"  Angle[°] = "+meas.toFixed(1));
  return meas;
}


// ------------------------------------
// simple parametric moving averager
// ------------------------------------
function sma(period) {
    var nums = [];
    return function(num) {                 
        nums.push(num);
        if (nums.length > period) nums.splice(0,1); 
        var sum = 0; var n = period;
        function sum_num (n) { sum+=Number(n); };
        nums.forEach(sum_num);
        if (nums.length < period) n = nums.length;
        return(sum/n);
    }
}

var sma16 = sma(16);

Input[V] = 0.494 Angle[°] = 15.6 Next reading = 15.6, SMA = 15.6
Input[V] = 0.496 Angle[°] = 15.9 Next reading = 15.9, SMA = 15.7
Input[V] = 0.495 Angle[°] = 15.8 Next reading = 15.8, SMA = 15.8
Input[V] = 0.495 Angle[°] = 15.8 Next reading = 15.8, SMA = 15.8
Input[V] = 0.495 Angle[°] = 15.7 Next reading = 15.7, SMA = 15.7
Input[V] = 0.498 Angle[°] = 16.1 Next reading = 16.1, SMA = 15.8
Input[V] = 0.497 Angle[°] = 16.0 Next reading = 16.0, SMA = 15.8
Input[V] = 0.495 Angle[°] = 15.7 Next reading = 15.7, SMA = 15.8
Input[V] = 0.496 Angle[°] = 15.9 Next reading = 15.9, SMA = 15.8
Input[V] = 0.495 Angle[°] = 15.7 Next reading = 15.7, SMA = 15.8
Input[V] = 0.495 Angle[°] = 15.7 Next reading = 15.7, SMA = 15.8
Input[V] = 0.494 Angle[°] = 15.6 Next reading = 15.6, SMA = 15.8
Input[V] = 0.494 Angle[°] = 15.6 Next reading = 15.6, SMA = 15.8
Input[V] = 0.495 Angle[°] = 15.8 Next reading = 15.8, SMA = 15.8
Input[V] = 0.495 Angle[°] = 15.7