Order of accuracy is a standard measure of the discretiza- tion error in a numerical approximation scheme. Scientists must know the accuracy of any numerical approximation, and often prove that the method satisfies the claimed order of accuracy manually, using math- ematical analysis. However, the actual code to implement the method might be more complex than the idealized method that was analyzed. We believe that the claimed order of accuracy of a numerical method im- plemented in a C program can be (largely) automatically verified using formal methods based on symbolic execution. The automation cannot be complete, because the problem is undecidable in general and because the programmer must provide some annotation to indicate the intent of the code. We give an overview of the technique, a demonstration of which we are in the process of implementing by extending the Toolkit for Accurate Scientific Software (TASS).