This lot of three slide charts is a must-have for anyone interested in metric conversion, lumber calculating, concrete estimating, or any other type of conversion needs. Made in the United States in the 1970s, these charts are a great addition to any collection of engineering and science memorabilia. The charts are perfect for anyone looking to quickly and easily convert measurements or estimate construction costs. Whether you're a collector, an engineer, or a contractor, this lot of slide charts is sure to be a valuable addition to your collection. Pre-owned from the early 70s in good shape. Previous owner's name written on front of one of them Please see pictures of actual items to be shipped