Those mysterious categories by which advertisers judge our social class have been laid bare in a booklet published this week.
It reveals that contrary to common belief nuns are very lower class, town clerks as posh as they come, and those in the rubber industry can consider themselves socially equal to CID detective constables.
The booklet by Carat, the media buying group, was published to provide a detailed guide to advertisers on the standard industry classifications of grade A (upper middle class), B (middle class), C1 (lower middle class), C2 (skilled working class) or D (semi-skilled or unskilled working class).
However, many distinctions appear bizarre. The research reveals that a nun of any denomination is a C1, university lecturers are grade B, rubber workers and RAF aircraftsmen are C2, but town clerks and senior retail buyers are A.
Meanwhile, the headmaster of a public or grammar school is not necessarily the town clerk's social equal. He or she is only an A if his school contains 750 or more pupils, while the captain of a merchant vessel only qualifies if the ship is 5,000 or more tons.
Farmers need not try so hard. They are upper middle class if they have 10 or more employees. But an editor or senior journalist on a national publication is upper-middle class regardless of circulation.
In the academic arena, only university professors and librarians in charge of "a really major library" make grade A. University lecturers are B, as are qualified teachers aged 28 or more, vicars, chief inspectors of police and banks clerks "with special responsibilities".
People classified as lower middle class include: curates, students who are on grants, radiographers, telephonists, driving instructors and foremen in charge of 25 or more employees, "doing mainly supervisory work".
Are you an overseer, a plumber, painter, bus driver, the owner of a shop with no employees or fireman? Then the marketing industry sees you as social grade C2.
London taxi drivers, bus drivers and shunters are also C2, even though bus conductors, traffic wardens, provincial taxi drivers and ticket collectors are a rung down the social ladder - grade D.
Religious distinctions are also surprising. Bishops and above are grade A, but ministers of "fringe free churches" and monks and nuns "without special responsibilities" are C1.