I have the following spreadsheet that shows the following and I need to fill
in column B with the reference number in column A and keep doing so if the
value is 0 until it changes to a new reference number and then and then that
cell has to be put in.

A1 B1
ref no ref no of A1
0 ref no of A1
different ref no different ref no
0 as above
0 as above and so on.
Does anyone know how to achieve this automatically. I can do it using the If
statement but these can be massive files and are for inexperienced users.
Thanks in anticipation once again