A value, expected to be close to the mean of a set of data, that is subtracted from each data item, so as to make calculations simpler. For example, suppose the data consist of the following values: 2001, 2004, 2007, 2007, 2005, 2006. Using a working mean of 2000, the data reduce to the simpler 1, 4, 7, 7, 5, 6, with mean 5. Thus the mean of the original data is 2000+5=2005.

In other cases a more involved transformation helps. For example, the x-values 19.42, 19.37, 19.88, and 19.62 are simplified by using the transformation 100(x−19) to give the coded data 42, 37, 88, and 62.