These are for performing an efficiency test to see if all of the oil being introduced into the burn chamber is being burned. If not you are wasting fuel, and are creating too much soot from unburned fuel.
A combustion analyzer determines proper parameters which fuel must be burned, and air is drawn into the burn chamber as well to aid in combustion. Once the installer tunes the equipment it can be quite efficient, but this eventually drops off and a year later service is typically needed with oil fired equipment.
Older boilers and furnaces can be quite inefficient, and here in New York we find many of the installers installed larger than needed equipment.
Meticulous Home Inspection finds issues like this on a daily basis, and we recommend only pro's check your heating equipment. But be wary of who you hire. Find references/reviews online.
Ray Wilson, president of Meticulous Home Inspection Corp. would be happy to answer any of your questions related to this blog, or inspection in general. Please call 631-902-6761 or see Meticuloushomeinspection.com