Clearly Perfect Angles Tool
Whenever a pattern tells you to draw a line.....DON'T!!
The CPA will be the most practical notion you've ever used! It "clings" to smooth sewing surfaces (no taping) so it's always in position ready to sew ANY 45 degree angle accurately. You will appreciate the Fabric Alignment Key and 1/4" & 5/8" seam guides. It's also color-coded for different techniques. And to answer one of the most common questions...No, it does not need to be removed to access your bobbin or move your table.
Do you have multiple machines? Are you looking for a gift? Do you have friends who would also benefit from the CPA?