Yet another calibration thing.

thingiverse

Regular calibration cubes may not provide the best calibration for a printer, as edges and especially bottoms can be distorted. Measuring overall size can result in slightly inaccurate scale determination. This model features lines and diamonds on both horizontal and vertical faces at 25mm spacing, with three variants uploaded. The complete corner option provides additional information, but the choice is yours. You can find other test patterns here: http://www.thingiverse.com/thing:23965. To slice accurately, ensure the layer height corresponds to the Z distance you'll measure. For instance, .4mm slices require 62.5 layers for 25mm in height, while 50mm needs 125 full layers. A .25mm setting is recommended, although .4mm vertical lines may slice strangely. Nonetheless, there should be enough marks for precise caliper measurements.