I have a work sheet that has 249 rows of data (user identification) (columns A thru F.

I would like to generate a random but unique 4 digit pin number for each row (result to be place in column G.

However there is a slight catch...

lets say I add 20 more users.. i want the pin numbers generated for them but not change the previous ones...

I figure it will ahve to be a UDF with a formula call so that it only triggers if a cell is changed.. (guessing here)...

Copying the data values to another sheet for 'storage' is an option, actually anything is an option right now.

Key things:
1. Once a pin number is generated it can not change for that user.
2. no two users can have the same pin number

Thanks in advance for any help with this