Some of our clients are physically crooked. They lean. They are bent.
How do we hem their garments straight? You have to get on the floor (Unless you have the privilege of a platform and a rolling stool).
I use a yardstick (or a foot long ruler for hems near the floor). I put a sticky note on the yardstick where the hem will lie in relation to the floor, and I use that as the gauge. Sticky notes are easy to see, easily moveable (for picky patrons*), and I don’t have to mentally remember the measurement.
* put a wide sticky note on the ruler and use a pen to mark the new measurement.