It´s easy to test without opening the covers.
Measurement may be 1,5433 V DC or so.
If there is the yellow "STORE"-key, press it and the display will show " S _ _ " .
Now you can enter a store-location between 5 and 29.
With the "ENTER"-key (key V DC ) the measurement will be stored.
Change the measurement - 0 V Dc or so.
Recall with "STORE" , "S _ _ " , "5" , "RECALL" (key kOhm) , the stored measurement will be shown.
If it works so, it´s a 7066 !
(or a KONTRON4066 or a R&S UDS6 ... or ? ?)
To tell the truth - I have the complete manuals - service and users ... BUT it´s not possible for me
to scan over 600 pages ! :'( AND I will not give them out of my hands.
If there are some fails or questions I will try to add the regarding diagrams - but it will take time !
regards James