... a swatch!
Yebb, that little cylindrical thing is a swatch!
Thing is. I was swatching my plötulopi knit double on 4.5 mm needles and got 15 sts per 4 inches (10 cm). I need to get 18.5. But the thing is I was knitting the purl stitches too loosly because I was afraid to break the yarn and it showed on the swatch. So I want to see what my gauge is if I knit in the round and lo and behold that little cylindrical thing appeared. I cast on 20 sts and knit around with the magic loop. It worked just fine and I got 18 (or maybe even 18 and a quarter) stitches per 10 cm/4".
I was really happy to have outsmarted the old swatch until I realized that the jacket I had in mind for the yarn was knit back and fro.
Back to the drawing board, maybe I´ll swatch again and this time be less lenient on the purl stitches.