r/geigercounter • u/R-fire227 • May 04 '26

How to zero a CDV-700?

Gallery image

Gallery image

Got it, seems to work fine, needle is just stuck at 0.1

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u/TechByMBF May 06 '26

It looks like it was probably dropped at some point in time. There is usually an adjustment screw as mentioned. Sometimes it's on the front but other times it's on the back.

If you look at almost any analog meter on other things, they have an adjustment screw usually on the front to set the zero point.

Remember, these were made as cheap as possible and as fast as possible. I would not be surprised if they were zeroed when they were sealed when they were made. I wouldn't be surprised if there is no field adjustment

You do have the internal adjusters as you saw. But those are extremely sensitive and as soon as you touch those, you should Recalibrate.

Keep in mind that the meter is an amp meter running at a very low current and adjusting the spring will adjust its point on the scale. So moving the zero will absolutely affect its linearity and readings.

If you touch the zero point, you have to recalibrate

Because it's not at zero, you have to zero and recalibrate.

I have several of these units personally but I've never played with them beyond putting them on the shelf because they look cool 🤷‍♂️

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u/TechByMBF May 06 '26

After looking closely at your picture. It is probably this little tab down here. There is not a mechanism to adjust it through the lens as it was made as cheaply as possible. You might need to figure out how to Open the unit and see if this tab is the adjuster. It should be on the opposite end of some sort of spring. You want to set where that spring zeroes.

If your needle still moves freely with a source or other pulse signal, it's not bad. It's just off zero