The MultiPhoton Correction (or Multiphoton PCA) is a SNOMAN processor used to measure the timing shift due to the multiphoton effect. The transit time spread of SNO's PMTs is about 1.5ns, and is measured by the regular PCA. If two photons strike a PMT simultaneously it is likely that one of them will arrive at the first dynode earlier than the other. The pulse from the first photoelectron will typically fire the discriminator, so tubes hit by multiple photons appear to have been hit earlier than tubes hit by a single photon. The MPC processor measures this timing shift as a function of charge, and the CAL processor uses this information to calibrate PMT times for high energy events. The multiple photon timing effect is the only timing effect for Monte Carlo PMTs, while for data the discriminator walk effect is also present. The Multiple photon timing correction for data involves larger shifts, as it must account for both of these effects.