I'm interested in finding an HP 571B digital clock.
This is a six-digit Nixie clock driven by a stepper motor
for counting. It appears to have been originally designed
as an option for early digital data recorders - a way to
timestamp measurements as they were made.
HP had a 570A as a plug-in for the HP 560A data recorder.
The 571A was a plug-in for the HP 570A data recorder.
[The data and image below were taken from HP's 1969 catalog:]
Indication: 6 display tubes to 23 hours, 59 minutes, 59 seconds;
12 hour format on special order.
Time base: front-panel switch selects:
(1) 60 Hz (50 Hz on special order),
(2) counter (1 pps, HP vacuum tube counters),
external (5 V positive pulses, 200 us long, 1 pps;
input impedence approximately 500 ohms).
Time-of-measurement accuracy: time recorded may be up to 1 second
less than correct time.
Print control: print rate controlled by clock or by external
device. Internally generated rates are 1 per second, 6 per minute,
1 per minute, 6 per hour, and 1 per hour.
Weight: net 20 lbs (9 kg); shipping 26 lbs (12 kg).
Power: ac and dc supplied by digital recorder; approximately 15 watts.