Download or read book 20 Degrees C -- A Short History of the Standard Reference Temperature for Industrial Dimensional Measurements written by Ted Doiron and published by . This book was released on 2007-07 with total page 24 pages. Available in PDF, EPUB and Kindle. Book excerpt: One of the basic principles of dimensional metrology is that a part dimension changes with temperature because of thermal expansion. Since 1931 industrial lengths have been defined as the size at 20 degrees C. This paper discusses the variety of standard temperatures that were in use before that date, the efforts of C. E. Johansson to meet these variations, & the effort by the Nat. Bureau of Standards to bring the U.S. to the eventual world standard. Illustrations.