Hello. This AGA 3100 by UEI - a current company -  has most likely never been used; it is so clean. UEI does not build it anymore, but I called them and they do service this.
When I called them the young man I first spoke to thought it was obsolete so, I was disappointed but I got a call back from an older tech whom queried me; he said they COULD celibrate ,inspect and repair...
I told him I wanted to sell it and he suggested getting 200 or 300 dollars for it and having the buyer send it in.
I bought it off e-bay and have never used it.
   It is a Nox analyzer.
   If you are curious, call UEI in Oregon...I want 200 dollars.
     On the off chance that it is not going to work I will refund OR if you want to cover the cost of repair I would agree to send it in and you pay for repair and shipping and tack on 200 dollars, after it is returned. It will come with it's blow molded case, manual spare filters and hoses no batteries. It is part number AGA 3100.

Nox are expensive sensors here also.

sorry this may be the wrong place to ask someone, what nox numbers would you expect to see on a gas anaylser on a good car?