Overhead Projection Versalog
Frederick Post model 1460DP [1969-71]
Teledyne-Post model 44AA-60R [1972+]
Hughes-Owens model 341 3738

Probably made in USA to Post's design.

Post's three overhead projection slide rules first appeared in the 1969 School Drafting Supplies Catalog, did not appear in the 1971 catalog and reappeared in the 1972 (Teledyne Post) catalog.

Each slide rule consists of two 12 x 7-inch sheets of lucite.  The bottom, stationary, sheet is printed with the scales from the slide rule stators.  The top sheet, which can move left and right, has the scales from the slide.   A 2-1/2-inch wide piece of lucite with a vertical hairline slides on top.  Light from the overhead projector passes up through all three layers.  Each rule came with a set of vinyl sheets which, when placed over the rule, mask out all but two or three scales.  These slide rules came with a one-page instruction sheet in an unusually sturdy cardboard box lined with red flocking.  The flocking leaves red dust everywhere.

The 1972 Teledyne-Post Slide Rule Catalog states "Each Overhead Slide Rule duplicates exactly the scales on the slide rules being used by the class ... including color coding."  I don't think this is true for the Versalog Projection rule.   The projection Versalog used the "IB" scale set (23 scales) in spite of the fact that the Versalog IB had been replaced by the Versalog II (24 scales) a year before the projection rule appeared.
!969 School Drafting Supplies Catalog, p 25