Holy cow, I haven't seen one of these in many decades. :O
The last time I saw one of these in person is when someone came to program our Mitel SX-50 at one of our hotels. The SX-50 has a serial port where a 'terminal' would interface and then you could print out the current registers and then change them if need be. This machine was so rare that the availability of people to program the SX-50 was basically zero and none.