I work from a Master list of customers that all have a pre-assigned numerical customer number. Every week I need to compare the Master with a separate Specials list that comes out that includes some customers who are already on my Master and some who are not. How can I compare the customers from the Master list with the Specials list? I want to call the customers who are on my Master first but who are also on the Specials list. Since the Specials list only applies usually for anywhere from one day to one week, I don't need to have these customers duplicated on my Master so it would be better to have a formula on the Master and not have to "merge" and then delete the information from the Specials list later. 
