manual: a wrong description in sample scripts

[wu liang]

Sir,
In the chapter "4.2 Increment a Number", it is said " The tn commands
are not necessary, but make the thing
 faster". However it is not correct in case that  all the digits is 9.
 For example, 999 will not get result of 1000 but 2000, if there is no
tn command,since it will be addressed again in the following s
command.

Best Regard,
Wu Liang