text: // required indicators
  let EMA = require('./EMA.js');
  
  let Indicator = function(config) {
    this.input = 'price';
    this.result = false;
    this.inner = new EMA(config.weight);
    this.outer = new EMA(config.weight);
  };
  
  // add a price and calculate the EMAs and
  // the result
  Indicator.prototype.update = function(price) {
    this.inner.update(price);
    this.outer.update(this.inner.result);
    this.result = 2 * this.inner.result - this.outer.result;
  };
  
  module.exports = Indicator;
  