text: module.exports = RunningMean
  
  function RunningMean(decay) {
    this.decay = decay && (1 / decay)
    this.mean  = 0
    this.count = 1
  }
  
  RunningMean.prototype.push = function(value) {
    var count = this.count
      , d     = this.decay || count
    this.mean = count === 1 ? value : (value + this.mean * (d - 1)) / d
    this.count++
  }
  