The Capacity coefficient is formally defined as C(t) = Hab(t) / [Ha(t)+Hb(t)], where H(t) is the integrated hazard function, and the subscripts ab, a, & b, denote the work done by both channels a & b, a alone, or b alone (respectively).

C(t) indicates the processing efficiency of a given system as we increase the workload -- for instance, by adding more to-be-processed items.
If C(t)=1, then the system is said to have unlimited capacity.
If C(t)<1, then the system is said to have limited capacity.
If C(t)>1, then the system is said to have super capacity.

[Ami; Oct. 27, 2007. Updated Oct. 29]