I'd been thinking about getting a differential manometer to check duct static and filter pressure drop,
and then I found a used C75 combustion analyzer that I can pick up for about 1/3 of new. Would be fun to play with if it also does temperature and manometer readings.

Any particular shortcomings compared to a Testo for example?
Keep in mind that I don't need it to do real work, just for education and entertainment purposes.

EDIT:
found the UEI web site, and it looks like the C75 doesn't do differential pressure but the C125 and C155 do?