I thought I was cutting them at 3-1/2 inches. Good thing I had extra fabric.

Sorry, I'm old school.

But here's perhaps a newer version;

Measure with a ruler, mark with a paintbrush, cut with a backhoe!

Anthony's Law of Force:
Don't force it; get a larger hammer.

Anthony's Law of the Workshop:
Any tool when dropped, will roll into the least accessible corner of the workshop.

Corollary:
On the way to the corner, any dropped tool will first strike your toes.
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Uncle Ed's Rule of Thumb:
Never use your thumb for a rule. You'll either hit it with a hammer or get a splinter in it.

Any part that is vital to the operation of a machine will spring off said machine and go into a time-space warp, disappearing completely.

ten lbs of shit in a 5 lb bag.