EKCO meter survey RADIAC NO.2 roentgen meter

[pvb]

I have a simple question but finding the answer is allot harder than I thought.

I have a EKCO meter survey RADIAC NO.2 roentgen meter: link
with this manual: link

But mine is missing the 30v / 9v battery holder... Does somebody know what the polarity of this battery holders 3 pins are?

Thanks in advance