is how long the person holds onto their reaction. Melancholies and Cholerics, for instance, will hold on to reactions such as anger, such that it often characterizes their temperament. Sanguines and Phlegmatics will get over reactions quicker, and thus generally come across as more friendly. (Since Sanguines will also get over pleasant reactions quickly as well, they seek constant stimulation).
This also became known as responsiveness
(not "reaction", though it deals with reactions). Sanguines and Phlegmatics tend to be more responsive to people, and Melancholies and Cholerics less so, as they are more focused on tasks. So this also is people vs task
orientation. It also corresponds in the Interaction Styles model as directing vs informing
. Those with longer sustain will tend to direct, while those with shorter sustain will tend to inform. It can also loosely match "Neuroticism", but in the FFM it is actually a closer match to Agreeableness
Again, in five temperament theory, the Phlegmatic is moderate in the scale, while Supine is high.