Commodore PC 40 - Page 249

You must use two percent signs (% % ) so that one will remain
after the batch parameter (%
0 - % 9) processing is complete. If
you had only %/, instead of % %/, then the batch parameter pro-
cessor would see
the %, look at/, decide that %/was an error
(a bad parameter reference), and throw out the %/ so that the
for command would never see it.
If the for command is not in a batch file, you should use only one
percent sign.
Batch Processing 111 I