The terrain ruggedness index (TRI) shows the elevation difference between adjacent cells (Moore neighborhood) of a digital elevation model (DEM). TRI is simple to calculate using the published equation. However, this publication contains some errors. First, the DOCELL command in figure 1 is wrong, as noted in the Erratum. But second and more crucial, the examples in figure 3 are wrong, too. This is not noted in the Erratum. Now, a colleague of mine implemented this index and used the examples to write his/her tests. Let me say he/she was majorly successful in making the implementation comply with the incorrect examples. I am grateful that neither we nor the authors work in a field on which people’s lives depend. But wait, what about Boeing…