All Plastic:  Frederick Post model 1445P  [c1968]
                  Similar to Hemmi model P45K

The difference between the Post and Hemmi rules is that the DF/CF scales on the Post models are folded at p; DF/CF scales on the Hemmi rules are folded at 3.16 (square root of 10).  All rules have inverted S and T scales.

Model 1445 first appeared in the 1969 School Drafting Supplies catalog and remained until the end of productiuon.  I'm not aware of model 1445P in any Frederick Post catalog.  I suspect that, at least sometime, it was what you got when you ordered a Post bamboo model 1445.  When would that have happened?  The 1965 date code on the specimen shown below implies 1965 or later.  I have arbitrarily asigned dates in the cross reference spreadsheet.

Model 1445P is an "open body" slide rule.  The full length of the back of the slide (except what is hidden behind the end brackets) is visible.
 

1969 School Drafting Supplies Catalog, p27 "A Teledyne Company"

1445 (left) date code "QJ" (October 1966) 1445P (right) date code "PB" (February 1965)