You can create a simple blend on customer id between master and facility. Drag customer id from master on row and also customer id from facility to row then also customer id from facilty to filter and select NULL
ither way to use is
ATTR(cust id master)!=attr(custid facilty)
drag to filter and set TRUE
before that only bring custid from master to row
Thank you for your suggestion. Could you please let me know how to get the count of the customers that were not served last year in a calculated field.