Here we have a vintage 1972 Sterling Plastic slide rule. Model #689. I already have the 6"carded Model #687 and some of the 11" Sterling Plastic slide rules but they are not carded. What a find. For some history, in 1968 Sterling Plastic bought ACU-Rule MFG.Co and added their line of higher end slide rules to the Sterling name. One to look for would be the ACU-MATH 400. The #400 slide rule is a good one but I still like the original Sterling ones.It was not long after in the 70s that the writing was on the wall for slide rules. Here comes the pocket calculators. This 1972 Mannheim model #698 was just about at the end of the road for Sterling Plastic slide rules. Earlier in 1970 Sterling Plastic was bought by Borden. A plastic US made slide rule should be in your collection.