1. The cursor to this rule was made by Keuffel and Esser - whether or not they made the rule itself, I don't know.

2. The trig scales are on the slide, and used with the D scale, which is an advantage for some forms of calculation.

3. This rule may have been made by Ricoh - the scale arrangement of the detail back left is identical to the Ricoh 153 and the end braces are also very similar and Ricoh is known to have made rules for Dietzgen. On the other hand, the rule specifically says "Made in U.S.A.". So, despite the similarities, this rule was probably not made by Ricoh.