The ornamental design for a protractor-ruler, as shown and described.
The sole FIGURE is a top plan view of a protractor-ruler showing my new design. A bottom plan view is omitted as it would be identical to the top plan view. Front, rear, and side elevation views are omitted as the protractor-ruler has a negligible thickness. The broken line showing is for the purpose of illustrating portions of the protractor-ruler which form no part of the claimed design.