DOn't expect toooo much from sniffers. They're temperature sensitive, all sorts of smelly things set them off, even leak detection fluid, and you can wallk into a room reeking of gas and they won't register any increase over outside. That's not to say they aren't useful. The cheapo pen style ones are good value if not quite as sensitive.
20mbar a minute you should be able to smell, or even hear! CHeck the flexy connectors on the meter, they can split, as can meter cap rubber washers.
20mbar a minute you should be able to smell, or even hear! CHeck the flexy connectors on the meter, they can split, as can meter cap rubber washers.