Nestler No. 23RF
- Type: Closed Body Rietz
- Size: 11 Inches / 27 cm
- Material: Mahogany and celluloid
- Front: cm / K A [ B CI C ] D L | 1:25
- Back: [ S ST T ]
- HvH: 1833
Has a centimeter scale on top and a 1:25 scale on the bottom. The centimeter scale is continued inside the body. For measuring things longer than the rule, one is invited to remove the slide and lay it end-to-end with the body.
Front scales are not labelled. The ST scale is marked "S&T". The rear has some physical constants and materials properties in German. The rule seems to have an expansion joint, a slit in the celluloid on both sides of the body. You can see its position in the reverse picture.
The rear windows are oddly offset. You can't see the T scale on the right hand end, and you can't see the S scale on the left-hand end. The trig scales are read on the C scale against the right index.
I'm given to understand that the Nestler No. 23 was the preferred slide rule of Albert Einstein and Werner von Braun. Well, if it's good enough for them... Actually, it's pretty amazing how often this rule has been copied over the years.
In black paperboard case. The stationer that originally sold the rule applied an address label for future reference.