ADS1115 analog gain signal module - how to run it with espruino?

Update this gives me the correct voltage in but I don't understand why?
Gain is 4096 & voltage multiplier 6.144

I2C1.setup({ scl: B6, sda: B7 });
var ads = require("ADS1X15").connect(I2C1);
ads.setGain(4096); 

setInterval(function(){
  ads.getADC(3, function(val) {
      console.log("val:"+val+" v:"+(val*6.144/32768).toFixed(3) + "v");     
  });
},3000);