Notes: "Two slide rules by Blundell Harling, an S143 and an S150. The S143 is essentially a Mannheim with no trig scales, and the S150 is a Rietz. Both slide rules are constructed of plastic in the manner of a duplex slide rule (i.e., the slide is fully exposed on the back), but the back is completely blank. The small “ears” at each end of the rules are cursor stops"
