For knitting projects that are knitted in the round, it really does make sense to knit your gauge swatch in the round. We all tend to knit or purl with different tensions. If you make a swatch knitted flat and a swatch knitted in the round, you will see that there will be a big difference in gauge. Instead of knitting a giant tube, I have learned neat technique of an easier way to swatch in the round.
First you will need either double-pointed needles or circulars. I am using these snazzy looking
Knitter's Pride MarblZ. You want needles that have no ends.
Cast on desired amount of stitches.
So instead of turning your work for the next row slide all of the stitches to the other end of the needle, just like making an I-cord. Since I am using dpn's, there was no need to slide my stitches. Bring the yarn around the back of the work and work across with right side facing.
You continue knitting only on the right side of your swatch. The working yarn is carried across the back. Now when you are done, bind off. Don't worry, if your yarn strands are not loose enough. You can cut the strands in the middle to get your knitted swatch to lay flat.
Soak your swatch in wool wash. Roll your swatch in a towel to absorb the excess water. I like to pin down my swatches while they dry. Here I am using
Knit Blockers on a Lace Blocking Mat from Knitter's Pride. The Knit Blockers are real time savers and I like how quickly I can get straight lines with them.