HP Model 4935A is a Transmission Impairment Measuring Set (TIMS) which measures wideband data and voice impairments. The frequency range over which measurements are made is 20 Hz to 110 kHz, in steps of 1, 10, 100, 1000, or 10,000 Hz There are four permanently stored, fixed frequencies 404, 1004, 2804. and 2713 Hz. Any other four frequencies may be temporarily assigned and stored by the user.