With version 5.10 of Turbo Calc, the program has become big enough
that it was necessary to use overlays.  The overlay file is the one
with the .000 extension, it must be in the default directory when the
program is started and it must remain available while the program is
executing.  However, you may change directories after starting the
program, Turbo Calc automatically returns to the original directory
to get its overlays.

Good Luck,
Paul Meiners