For somebody who knows electronic terms in European languages.

I am trying to identify the country of manufacture of an electrotherapy instrument probably manufactured early last century.

Some numbers written in pencil on the inside of the wooden cabinet and a drawer put a line across the stem of the number 7. This is of course a European way of writing a number.

Each of four brass terminals has a label in the form of a letter stamped into the wood:

1. What is probably the positive battery terminal has the letter 'K'.

1. The other battery terminal has the letter 'Z'.

2. One pole of a switch (function unknown) has the letter 'P'.

1. The other pole has the letter 'S'.

Can somebody identify what words these represent? I have looked in German and French dictionaries and cannot get any sense from 'positive', 'negative', 'on' and 'off'.