The block of information for a target in the `library' file starts with a target directory, and this is followed by the actual data. The target directory is read from the `library' file by the subroutine trghdr, and it is stored under the equivalenced arrays nhead and xhead. Each item in the target directory (REAL or INTEGER) is 64 bits long, and this fact makes for portability problems. The form of the target header is as follows. The information presented here is derived from the note [5] by Rathkopf.