MakeIndex types out on the terminal the number of lines read and written and how many errors were found. Message to identify the error are written on a file with extension ilg. There are two phases in which MakeIndex can produce error messages: when it is reading the idx file, and when it is writing the ind file. Each error message prints the nature of the error followed by a line number, identifying where in the file the error occurs. In the reading phase, the line number refers to the idx file; in the writing phase, it refers to the ind file.