This is a vintage Keuffel & Esser Slide Ruler with a leather case, model number 4150-1. Made in the United States, it is a wonderful collectible for those interested in engineering or science from the 1930s to now. The ruler is in good quality and comes with all of its original parts. It has been well-preserved and is perfect for display or use. The leather case adds a touch of elegance to the ruler and has kept it protected over the years. This is a great addition to any collection and a must-have for slide rule enthusiasts.