A Better Ruler?

I have a two metal straightedges, one is used more than the other.

The upper straightedge has a rounded lip on the right and left sides.
The ruler marks start inside the rounded end, about 1/8" in.
The markings on the bottom ruler start right on the flat side.

I use the bottom ruler more often.

TIP: Here's a way to check the spacing and straightness of centering rings on an engine mount.
Both centering rings are glued 1/2" from the ends of the tube.
Using the squared ruler against the ring I can easily check the 1/2" spacing from the ends of the motor mount tube.
If the ring is flat against the end of the ruler I know it is perpendicular to the tube.
Rotate the tube and check again from a few different places.