it's about $200/pop to set up, but thereafter it ought to be less than $30/crop for me to run. The retun looks like it will be worth it.

And yes, a meter is the only way to tell how much you're getting into the atmosphere -- or you could put the neighbor's cat in there and see when it dies. But what help is knowing if you can't regulate it? The logic of this approach escapes me, even after trying it . . .