ABSTRACT
It has been my experience, as well as many others who have looked, data is generally much less accurate than it is advertised to be. This is not a trivial point-we depend on initial data for many decisions, as well as for the input data for simulations which result in decisions. Since the errors are of so many kinds, and I have no coherent theory to explain them all, I have therefore to resort to isolated examples and generalities from them.
