Also known as: Swatching for circular knitting.
A gauge swatch has to be knit using the same techniques that will be used for the final fabric. Many, if not most, knitters have slightly different tension for their knit and purl stitches. This means that stocking stitch when knit flat (as alternating rows of knit and purl stitches) will have a different gauge from stocking stitch knit in the round (where every row is knit).
This article describes how to produce a gauge swatch for a fabric that will be knit in the round, regardless of whether circular needles or double pointed needles will be used.
How to do it
See the links below.