An error or inconsistency discovered by the program is assigned an integer error code from 0 to 4. If the error code is larger or equal to the value of ERRTOL, the program will stop. The meaning of the error codes are: 0; information, 1; warning, 2; error (this is the default), 3; severe error, meaning that the results cannot be trusted, 4; fatal error, the program will always stop. For ERRTOL > 4, ERRTOL is set to 4. For ERRTOL=-1 all errors will be ignored and the program will continue.