Older 6.2 solarmeter in the black/gray color question

Do these work just as well as the newer green 6.2 models? I'm getting the older version. I want to make sure it's going to give me the right reading.

& how would I know that it's giving me the right reading?

How long do they usually last?

Thanks!

I contacted the guy who makes them, because I bought a used 6.5 and 6.2 and was wondering the same thing.

Here's what he said when I asked how to test the 6.5:

They generally hold their settings virtually forever. Check accuweather UV Index forcast for a noon clear sky day and see if meter reads close to forcast. Stand out in open away from any buildings and trees so meter has a full-sky view.

IF it's way off... we do recal for $75.