The vintage slide rule is an ACU-MATH no. 400 model made of plasticm, measuring 12 inches in length and 1-5/8 inches in width. It comes with a case/sleeve for protection. The slide rule features scales B, CI, and C on the slider, and scales S, K, A, D, L, and T on the face. Back face has equivalents, decimal fractions , and trigonometric functions. Made in the United States, this collectible piece is designed for engineering and scientific calculations, reflecting the precision and craftsmanship of slide rules from the mid-20th century. This collectible slide rule is likely from the engineering or science field, dating from the 1950s to the present day. The slide rule was a common tool for calculations before the widespread use of digital calculators, making it a nostalgic piece for those interested in the history of mathematics and technology. Similar slide rule helped put first man on moon (NASA). Pre-owned by engineering student in 1970s, stored in leather sleeve, works as supposed to See pics for detail. [e-01]