Here we have 4 newer Concise slide rules, made in Japan. They are close to knew and are all different. There is the BMI rule and the well known small 28N but there also is the larger 300 log-log model with many basic calculating scales on both sides and last but not least the 480 which has a mathematical side with A,D,C,B,K,L and Ci scales for basic calculation and a full calendar on the other side which makes planning calculations. The 480 model and 28N come with their manual (Japanese / English). For reference, the 28N (yellow) measure is 8 cm or 3 1/4 inches in diameter. Check the attached video on how to work your vintage man tool : slide rule operation instructions!
