Bottom edge: 0-28 cm (Vertical)
Back of slide: [S, S&T, T]
Back of rule: THE FREDERICK POST CO. NO. 1455, Table on plastic.
This page is from the 1936 (18th Edition) Post Catalog. Post used the term "Universal" for many of their better quality products.
The catalog shows // A, DF [CF, CI, C] D, K & [S, L, T] ||. If you have a specimen with the same scales as the catalog please let me know.