Ronda's Mini Arc
This little curved ruler is great for small places and continuous curves. The outer and inner curve are each a different size curve and this 1/4 inch thick ruler is easy to hold and small enough to manipulate among the folds of a large quilt. It is small enough and the curves are open enough that it can even be used with low shank machines along the sides and front without issue, though it most likely won't fit behind the foot. Etched markings run along the 2 curves for 1/4 and 1/2 inch spacings. Two different curves and low price make this a great starter ruler. It even has a handy hole for hanging the ruler up for storage.