Method and apparatus for the stepwise movement of items

A sample analyzer for analyzing the characteristics of a plurality of samples. The analyzer includes a movable sample support for holding samples arranged in a first plurality of holders in a sequence for movement in a first direction. An indexing drive for the sample support advances the sample support in the first direction in a set of one or more increments, wherein one increment in the set is a net amount equal to a second plurality of holders greater than one holder and less than the first plurality such that the second plurality is relatively prime with respect to the first plurality.