Farallon gauge question

[ew1usnr]

What is the screw on cap for, on top of this Farallon console? I'll post another photo following this of the interior. It has what looks like electrical contacts inside.

 

[ew1usnr]

Here is the inside under the screw cap. It has a spring in the center, a copper strip on the side wall, and the lid has a metal plate on the underside. They look like electrica contacts. What could have gone here on top of a pressure/depth gauge console?

 

[canuckdiver]

I'd just be guessing, as I don't know the product, but it looks like a battery holder for some kind of button cell battery.

A backlight for the guage???

 

[ew1usnr]

It's an illuminated gauge. I bought that off ebay because I needed a pressure gauge. This one is neat because it also has a 300-foot depth gauge on the back, making a compact console. I saw that scew cap in the ebay advertisement picture, and assumed it was for mounting a compass. I got it in the mail today and it had me puzzled. Now that I know what it is, it should have been obvious. But I just didn't think of an illuminated gauge.
Anyway, I looked through the the Skin Diver magazine collection at the USF library tonight and found a write-up on the "Farallon Illuminated Diving Instruments" in the February 1973 issue. Cool!!! I'll get a battery for this gauge and try it out.

 

[canuckdiver]

cool, looks neat bud, be sure to let me know how it works out!

 

[Paul Perkins]

Can anyone tell me what battery the Farallon Pressure Gauge takes for the light?