This paper d erives numerical bounds for t he error, in c!'r tain closed regions, of th e differenC'e analog of the Dirichlet problem. It is concerned only wi th the difference between the exact solut ion of the differen ce equation and t he solu t ion of the D irichl!'t proble m. The error bounds obtained involve quan tities which can a ctually b e computed , such as t he mesh size, and t he oscillation and modulus of contin uity of t he gi ven fun ction on t he boundary. So far a s t he m ethod is concerned , t h e chief novelty is t h e use of the difference analogs of harmon ic mea sure and t he Schwarz Alternatin g Process.