I have something that is a yellow steel box, called a civil defense
radiation detector.

http://www.radmeters4u.com/cdv715-new.jpg

I only have the yellow box.

No matter what I do, I cannot zero the thing. The needle goes all the
way to the right to Circuit Check. Does anyone know how to fix that.

I fully realize that the meter has an inappropriate range. So if you
feel like pointing it out, I know that already.

i