Q:

what do the numbers in VERSIONs mean?

I mean for example if a software has this number in its version 13.0.5 and another version has 13.0.5.1 or something like that what is that zero for?what does this zero show?
Is there a rule for these numbers?

A:

Yes it appear because there is a revision number after it. If it's been 13.0.0 then that'll be 13.0 . Major and Minor revision must always show, but the revision and build number are not mandatory.
That said, there's many ways to manage version numbers.
This should help you figure out : http://en.wikipedia.org/wiki/Software_versioning
Hope that help.

A:

The Wikipedia reference from Marc on Software Versioning is good,
and you might also like to read Jeff's post on What's In a Version Number, Anyway?.
While we are at this, the Ubuntu scheme is fun and neat too.

