ECG CALIBRATION: Two reports, one at 1mV/10Hz signal source traceable to NPL standards and the other one at 1mV/1Hz signal source (uncalibrated) on the calibration of 12 leads ECG machine were prepared for the uncertainty measurements. The bio-simulator producing sine, square and triangular waveform at 1mV with variable frequencies got calibrated against a primary standard source of 1 mV/10Hz at NPL and subsequently put in use as a secondary standard source for further calibration of ECG machines.