A blood pressure monitor, particularly of the type having an inflatable cuff communicating with a pressure sensor and suitable for home use, may be calibrated by applying a sealed canister containing gas at a known pressure to a port so as to apply the known pressure to the pressure sensor, and comparing a pressure signal from the pressure sensor with the known pressure so as to determine a calibration error of the sensor and/or adjust the calibration of the sensor, e.g. by electronically adjusting the sensor. Several canisters may be used to calibrate the sensor across a range of pressures, each canister having a different known pressure. Each canister is preferably ruptured when attached to the port and is not re-usable, and may comprise an identifier such as an electronically readable identifier which is stored in a memory in association with the value of the known pressure within the canister. Temperature sensing means may be provided whereby the pressure reading is adjusted to compensate for temperature, e.g. of the gas released from the canister. The monitor may comprise means for sensing mechanical shock and alerting a user or remote monitoring personnel to provide an indication that recalibration is required.