The Fireworks Pullover pattern includes two gauge options: 20 stitches in 4 in/10 cm and 22 stitches in 4 in/10 cm. If you find yourself between those two gauge options, we recommend either swatching again with a needle one size smaller to aim for the 22 stitches in 4 in/10 cm gauge. Or you can go the other direction and swatch again with a needle one size larger to achieve the 20 stitches in 4 in/10 cm gauge option. Having two gauge options available creates a wider range of sizes, so – if in doubt – look for the finished measurement you wish to achieve, and (if there’s more than one option for gauge) choose the gauge that will allow you to achieve the finished measurement you want.
For help knowing how to modify patterns and make adjustments for various gauge options, especially for patterns that may not have more than one gauge option available, we recommend the Sweater Boss workshop, which provides more detail about pattern math and how/where to make adjustments.