The perturbation of off-energy functions in the arcs affects the SLC performance in two ways. First of all, it introduces additional emittance blow-up in the arcs through synchrotron radiation loss. Secondly, if the perturbation is too large, the chromatic correction in the final focus cannot completely suppress the eta at IP resulting in a larger beam size. Both effects reduce the luminosity. In this report an analysis is made of the disturbances to the horizontal eta-function generated by imperfections in the arcs ad their effects are estimated. Show Partial Abstract