Methods of calibrating a Time of Flight (TOF) mass analyser comprise performing a plurality of calibration analyses of calibrant ions using the TOF mass analyser, each calibration analysis measuring flight times of the calibrant ions. The TOF mass analyser has an associated instrument parameter which effects the flight times of the calibrant ions. Each calibration analysis also comprises determining a reference calibration curve based on known mass to charge ratios of the calibrant ions and the respective flight times, wherein the reference calibration curve is associated with the instrument parameter for the respective calibration analysis. For each calibration analysis, a value of the instrument parameter of the TOF mass analyser is different. A calibration curve for use in a TOF mass analysis performed by the TOF mass analyser can be determined based on the plurality of reference calibration curves and the instrument parameter.