Residual errors in photomasks have triggered development work for correcting mask manufacturing effects. Long range and short range effects contribute to the observed signatures. The dominating error source is the etch process and hence it was captured with a variable etch bias model in the past. The paper will discuss limitations and extensions to the approach for improved accuracy. The insertion of MPC into a post tapeout flow imposes strict requirements for runtime and data integrity. The paper describes a comprehensive approach for MPC including calibration and model building, model verification, mask data correction and mask data verification.