What Pluto governs
Pluto covers power and its use, compulsion, what is hidden and later exposed, and any process that destroys something in order to replace it. It also takes the shared and involuntary side of life: inheritance, debt, and the parts of a situation controlled by someone else.
The specific quality is that Pluto contacts are not optional. Uranus removes something quickly and Neptune blurs it, but a Pluto contact reworks the thing from underneath and the person does not get to choose when it stops.
An uneven orbit
Pluto takes about two hundred and forty-eight years to circle the zodiac, and its orbit is markedly elliptical, so the time it spends in a sign is not constant. It moves quickly through the signs near its closest approach and slowly through those at the far end of the orbit, with the result that a sign can hold it for as little as a dozen years or as long as about thirty.
That unevenness means Pluto cohorts are not equal in size. Some Pluto signs cover a decade of births and others cover a generation, and comparisons between them are not comparing like with like.
The house, and the degree
Because the sign spans so many births, the individual reading rests on the house and on the aspects Pluto makes to the Sun, Moon, angles and personal planets. The house says which area of life is subject to a process the person cannot call off. Pluto in the eighth house takes that to shared resources and mortality; in the third to speech and siblings; in the sixth to work and the body.
All of this needs a birth time. The angles move about a degree every four minutes, so an approximate time can place Pluto in the wrong house entirely, and the reading changes completely when it does.
Rulership and dignity
Modern astrology assigns Pluto the rulership of Scorpio, which traditionally belongs to Mars. Both are worth checking, and they answer different questions. Mars describes how a Scorpio placement acts, Pluto describes what it is compelled towards.
Pluto was discovered in 1930 and has no classical dignities. Various exaltations have been proposed, most often Aries or Leo, but none has become standard and a chart report listing one is following a single author's preference.
Retrograde, and the reclassification
Pluto is retrograde for about five months a year, so roughly two in five charts carry it. As with the other outer bodies, that frequency is too high for the condition to distinguish anyone.
The 2006 decision to classify Pluto as a dwarf planet was a change in astronomical nomenclature. Astrologers had already been using bodies that are not planets, including the lunar nodes and a number of asteroids, so the reclassification changed the label and not the practice.
Questions people ask about this
How long is Pluto in one sign?
Between about twelve and thirty years, because the orbit is elliptical and its speed varies considerably.
Does Pluto still count if it is a dwarf planet?
Astrological practice did not change in 2006. Astrology already used the lunar nodes and asteroids, none of which are planets either.
Does Pluto rule Scorpio?
In modern practice yes. Traditionally Scorpio belongs to Mars, and reading both gives more than reading either alone.
Is my Pluto sign personal?
No. It covers at least a decade of births. The house and the aspects to personal bodies are what make it individual.