Amy, the decans are different than the triplicity rulers. The decans are 10 degree divisions of each sign, whereas the triplicity rulers govern three signs of an element. As an example, say Aries was your 5th house (daytime), it is a fire sign so the three triplicity rulers would be (depending on your system of choice) the Sun, Mars, and Jupiter. So, you would look at their conditions in your nativity (essential and accidental dignity, aspects, etc.) and they would respectively describe your children, pleasure(hobbies), and emissaries or embassies(?). I think some of these could be modernized with research, as emissaries don't really have that big of an effect on our lives nowadays. I have also seen where these could be used to describe all the significations of a house but in the periods of life, i.e. first trip ruler is first half of life, second is second half, third is common to both, similar to the method of observing the triplicity lords of the luminary in sect to find out general happiness and conditions of life, which is a Hellenistic concept...
