Martin (1992: 533):
The basic realisation principle associated with affect is amplification (see Table 7.14). Like a stereo system, affect is something that can be turned on or off and balanced between speakers (both off, one on, both on) and whose volume can be adjusted to normal listening levels (predisposition) or turned on really loud when the occasion desires (surge).
This continues the misconstrual of affect — a charged or neutral relation between interlocutors — as the behavioural surges or predisposed reactions of individuals. A given text realises a situation with either charged or neutral affect, as one dimension of the tenor relation between interlocutors.