A sample holder for use in a centrifuge, the sample holder being generally planar and comprising: an aperture or recess for releasably retaining a sample storage member including a sample chamber adapted to contain a volume of liquid； a centre point around which the holder will rotate during use； and one or more calibration features, wherein the calibration feature(s) comprise one or more outer edges, which lie on the side of the or each calibration feature which is furthest from the centre point, and the one or more outer edges comprise a series of radially spaced-apart outer edge portions or positions which are spaced at different distances from the centre point as a function of angular position around the centre point.
