Frederick Post Models 1447D and 1447DA Classroom Demonstration Rules

These were large slide rules carrying the same scales as Frederick Post model 1447 Student Slide Rule
They were made of painted softwood--probably in the United States.
They don't appear in any catalog or dated material: I guess they were available from about 1950 to 1960.

Here are pictures of specimens the Slide Rule Trading Co sold many years ago.  I apologize for the quality.

Model 1447D

Model 1447D:  Overall length 48",  Scale length 42-3/8"

Model 1447DA

Model 1447DA:  Overall length 72", Scale length 63-1/2"