german pressure meter ??

[model40]

hello, found this the other day, i dont realy know what it is, if you could help me, that would be great
any way found this in a french jumble sale, it looks about the right time for ww2 , bakalite nut on it and the glass is very old looking, amazing that its not broken , the paint aswell is exsactly the same as other things in my collection. any way for you to diside here it is

[Tom2]

Perhaps an electro mechanical guage? Looks like Kg/cm or something at the bottom of the dial, but the label on front seems to refer to electrical specifications. Seems a bit more complicated than a common pressure guage, and it does appear old. Perhaps some other external markings are obliterated.