5-Inch "Commerce" Slide Rule
Frederick Post model 1444D [1944-45]
Same as Roos PSR-105   ("Pocket Slide Rule 105")

Back: USBS Circular 47 on paper 
On Roos-made rules the red ink fades easily and celluloid facings turn very yellow. 


Excerpt from 1945(?) Price List
Second price listed is per dozen.

 Catalog doesn't mention "Commerce" but it is printed on the slide rules.

Most Frederick Post  Roos-made closed-body rules appear in two versions--with and without a "D" suffix on the model number.  I don't know of any specimens or documentation of this particular model without the "D" suffix but I expect some rules marked just "1444" exist.