srecord Frequency(double frequency) is Comparable<Frequency> {
  gettable double interval;
  
  double frequency() { ret frequency; }
  
  *(double *frequency) { interval = doubleRatio(1, frequency); }
  
  toString { ret frequency + " Hz"; }
  
  public int compareTo(Frequency f) {
    ret cmp(frequency, f.frequency);
}