And as a quilter I know this... a quarter inch seam is usually a scant quarter and even that isn't cast in thread.
There are lots of things that effect that scant quarter - and those are the things I wasn't taking into consideration yesterday when I sat down to sew the nine patch units for Double Delight. My biggest mistake was not sewing and CHECKING a complete unit. I was so happy to just be at the machine... I was just sewing, and sewing, and sewing! Then I measured... uuugh! Then I cut new strips... tested and sewed and measured again and then sewed a complete strip set to measure.
On the left is what I made a bunch of... on the right is the correct size... yeah - there just isn't any way to stretch out that nearly 1/4" of missing width.
My modern machine has the ability to move the needle sideways - I usually have it set to the right at 3.0 to achieve a scant quarter. That is what I used to sew all these strips... which I'll set aside to use for something else.
So how'd I screw this up so nicely? Many of the fabrics I'm using have some heft to them (both in weight or sizing) AND the thread I was using is a bit thicker (a coats & clark 100% cotton - I usually use an Aurfil for piecing)... both factors that play into your seam allowance... and if you have multiple seams that are off just a tiny bit - they add up to a big difference.
I need to set my needle at 5.5 to the right to get my strip set to equal 3.5"
I dreamed about this all night long... a lesson I won't soon forget.