Specification for type of Mineral Oil

Hello from the great white north (suffering from the coldest June in recorded history here, so much for Global Warming but that's another topic ).

Just let me start by stating that I am not an engineer, so please type slowly as I do not read so fast.

I have a machine I look after at a Cu/Mo mine. It's called an "On Stream Analyzer" and it has a lot of pneumatic controls. While doing routine maintenance, I discovered that the "air oiler" was (embarrassingly enough to type) "empty". The following was written on the side of the container for the oil, and I'm at a loss as to what the last line means:

"INP. Max 16 Bar" (this I assumed was amount of air pressure allowed to use the unit)

"T. Max 50° C" (this I assumed was maximum temperature for the oil used)

"USE MINERAL OIL" (straightforward enough)

"3 to 10° E" (this is where I got lost)

After many a different google search, I cannot find the meaning of "3 to 10° E". It might have something to do with conductivity I believe, but I am really not sure. If any of you good folks would be so kind as to enlighten me as to its meaning, I would be most appreciative. Thanks for the help in advance and also thanks for all of the great reading (I catch up everyday with the emailers).

P.S. Sorry about placing this in the "general discussion" but I wasn't sure if I should post in "chemical and material science", "electrical engineering" or "instrumentation".