gas analyzers

[Faulkner]

Howdy!
Today, as I perused the stock at my local state surplus warehouse, I came across two "gas analyzer"s for $15 apiece. How do these work? What, specifically, would one use a gas analyzer for? Are there any specific things I should look for? Any necessary suporting equipment?
Thanks for the help!

[Chris Smith]

There are many types of Gas analyzers. What does yours say it is? CO, CO2, HC, NO, etc., etc.?

[russlk]

Gas analyzers are used to test tail pipe emissions of automobiles, among other uses. Annual testing is required in some states, for vehicles older than ?.