Ok. Thank you for your reply. Here are my Queries.
1) When the bezel of the illumination window is rotated to a certain angle, what look like 2 sockets for electrical wander plugs are revealed. I am guessing that these relate to an alternative electrical illumination system. Is there an internal electric bulb which is powered through these contacts ? I have tested with a multimeter; one socket is connected to the body of the theodolite, the other appears to be connected to nothing. Maybe there is a switch somewhere, or perhaps the bulb has blown, in which case how can it be replaced ? It is possible that the sockets simply receive a plug-in attachment and are purely mechanical in function ?
2) On the left-hand vertical support for the trunnion there is what looks like a locked adjustment screw, which in my instrument shows signs of rather rough usage. What is the function of this adjustment.
3) On the lower part of the instrument (the tribrach) there is a threaded nipple with a central screw-driver slot. What is the function of this ? Should it have a plastic cover ?
Just for the record, these questions are now answered. I consulted Nicolas de Hilster, who seems to be exceptionally knowledgeable about all matters thoedolitical:
"... the threaded nipple is where power comes into the instrument. It requires a special connector and battery kit to provide power. There are no light bulbs inside the instrument and indeed the two sockets at the illumination window will provide power to an accessory lamp. If you test the sockets you will find they are connected to the nipple.
I have attached pictures of a battery pack and the connector that goes into my total station. At the right hand side of the connector image you can see the same thread as that on the nipple. A dummy nipple on the battery pack allows the cable to be looped back to the battery pack, so you can use the cable as a handle to carry the battery pack.
The adjustment screw on the left hand vertical support most likely is the adjustment screw of the compensator for the vertical circle. Your instrument is a K1A, where the A stands for Automatic, automatic in the sense that the vertical circle is compensated and settles automatically to have zero at the zenith (provided that the instrument is levelled within a certain tolerance, normally when the bubble of the circular vial is within the engraved circle)."
