A method of calibrating a glucose sensor, which method comprises:(a) preparing a first glucose-containing calibration solution by combining water or an aqueous solution with alpha and beta glucose, the alpha and beta glucose being provided in solid form；(b) exposing a glucose sensor to said first glucose-containing calibration solution and determining the sensor output；(c) exposing the glucose sensor to one or more further calibration solutions having different glucose concentrations from each other and from said first glucose-containing calibration solution and determining the sensor output for the or each calibration solution； and(d) determining a calibration curve from the sensor output data collected in steps (b) and (c).
