At left is a top-down pullover knit on US 17 needles. The pattern called for Brown Sheep "Burly Spun" yarn and a gauge of 8 sts to 4" in stockinette stitch on US 17 needles.
I held together three strands of worsted weight yarn and knit a swatch of stockingette stitch on US 17 needles. I got 7 sts to 4". I figured the looseness was due to knitting back and forth (instead of in the round), so I soldiered on.
When I checked gauge again (which was when I was nearing the point of holding off sts for the sleeves), I was astounded to discover I was getting 8.5 sts to 4". Thus, a pullover that was meant to be 46" around (finished measurement) turned out to be about 42" around. (It should have been about 40.8" around by stitch count, but that didn't happen, either.)
I am flummoxed. I am finishing the pullover -- it's using up odd balls of yarn in the stash and God knows it will fit someone -- but this is driving me a bit nuts.
I am, however, rather proud of the color transitions, all of which are accomplished with changing out the various strands of yarn held together.