The model 213-3 is a simple interval timer. The model 213-4 is simple access to the host computer time clock. This implentation has no visible (GUI) component.

Both devices are at the address of 06/46. PDT 46 (input) instructions operate on the Time Of Day clock. PCB busy-check is a no-op, and PCB 06 interrupt control functions operate on the Interval Timer.

The time of day clock is presented as a formatted string, "HH:mm:ss.S". It is not known how the original hardware presented the time data.

The interval value for the Interval timer is assumed to be milliseconds, with an effective range of 0 to 262.143 seconds (4.37 minutes). It is not known what the actual units for the interval value were. This implementation defaults to (powers-up with) a time interval of 500 milliseconds.