When you measure to rotary cut, use the ‘skinny lines’ rather than the thicker ones on your ruler. The width of the line on the ruler can introduce inaccuracies, especially when you are cutting tiny pieces.
You DON’T need a special ruler divided into sixteenths to make the patterns.
Most rulers are marked with eighths of an inch:
A sixteenth is half of this:
Sew4Home.com has downloadable versions of these diagrams that you can print and put on your sewing-room wall!
So when you need to cut sixteenths, just eyeball half-way between the relevant eighths measurement:
On the rare occasion I call for a thirty-second of an inch (yes, they are in the more complicated patterns, sometimes), all you need to remember is that a thirty-second is half of a sixteenth.
So when you need to cut thirty-seconds, just eyeball a tiny amount past the mark, or shy of the mark; or, about a quarter of the way between the relevant eighths measurement: