Slony Local Node 0 disallowed?

I was experimenting with configuring Slony-I using pgAdmin 1.6.1 on
Windows 2000 Advances Server.

I thought it would be nice to use Node numbers to match the slave
numbers, i.e.

Local Node of zero for the Master, and one for the first slave, 2 for
the second, etc...

pgAdmin would not allow me to use zero for the master (it greys out the
OK button).

I had a quick look at the Slony and pgAdmin sites but I cannot see the
reason for this. Is there one?

Thanks,