We characterise explicitly the decidable predicates on integers of Infinite
Time Turing-machines, in terms of admissibility theory and the constructib
le hierarchy. We do this by pinning down zeta, the least ordinal not the le
ngth of any eventual output of an Infinite Time Turing machine (halting or
otherwise); using this the Infinite Time Turing Degrees are considered. and
it is shown how the jump operator coincides with the production of masterc
odes for the constructible hierarchy: further that the natural ordinals ass
ociated with the jump operator satisfy a Spector criterion, and correspond
to the L-zeta-stables. It also implies that the machines devised are "Sigma
(2) Complete" amongst all such other possible machines. It is shown that le
ast upper bounds of an "eventual jump" hierarchy exist on an initial segmen
t.