Since November 25th, 2004, the Sudbury Neutrino Observatory has been taking production data in its third and final phase. For this phase a ‘Neutral-Current Detection (NCD) Array’, consisting of 36 strings of 3 He proportional counters and 4 strings of 4 He proportional counters, was deployed in SNOʼs D 2 O volume. It supplements the Cherenkov detector, consisting of 9456 photomultiplier tubes, present in the previous two phases by offering an independent measurement of the solar neutral current rate. The 3 He counters detect neutrons from neutrino-deuteron neutral current interactions in the D 2 O. We describe the calibration of this array.