Some Fortran compilers (like Linux g77 ver.0.5.20, Linux fort77 ver.1.13, or very old HP-UX (ver.8) or Apple Macintosh compilers) do not adhere to the ANSI Fortran 77 standard to that extent they could correctly compile packages like MODEL or CRT (they incorrectly compile DO loops). HP-UX ver.10.20 compiler fort77 does not compile all programs correctly (problems with names of subroutines). Note that Linux compiler g77 ver.0.5.23 or ver.2.90.23 (980102) already compiles DO loops correctly and is used by the authors (option -O is not recommended). Linux fort77 ver.1.14a also compiles DO loops correctly but has other problems. The authors use compilers by Lahey under MS-DOS.