record(val) {
    this._buffer_interface[this._record_index] = val;

    // advance index
    this._record_index++;
    if (this._record_index > this._max_records) {
      // loop index around when reached end
      this._record_index = 0;
    }

    // track number of entries recorded
    if (this._num_records < this._max_records) {
      this._num_records++;
    }
  }
Records the next value and advances the record counter.
@param {Number} val