Before revision: In other words, the mirror has a finite output (or Norton) resistance given by the ro of the output transistor, namely: czy is sb where VA is the Early voltage; and VCE, the collector-to-emitter voltage of output transistor.
After revision: In other words, the mirror has a finite output (or Norton) resistance given by the ro of the output transistor, namely: where VA is the Early voltage; and VCE, the collector-to-emitter voltage of output transistor.