Reference Values Next is the question of where to get the value of the CTE for a specific material. There are a large number of reference books that give values for the CTE, and a number of WEB sites that are useful. At the end of this tutorial we have made a list of sources that can be helpful. There are two problems with most, if not all sources, of reference data. First, there is no estimate of the uncertainty of the values in the tables. This includes the uncertainty of the measurement as well as the batch to batch variation in a given material. Even fairly well defined materials, such as ANSI numbered steels, still have ranges of the various components in the material. Luckily, most heat treatments do not change the CTE radically, but there are very few sources that provide data to help us with that conclusion. Secondly, nearly all tables give the CTE as the average over some temperature range. In many cases you have to read the tables and footnotes carefully to find the applicable temperature range. An example of the problems in this area is shown in the next page. | 
