I have 4 fields, OCTET1, OCTET2, OCTET3 and OCTET4 where the first 3 fields are populated with values say 8 9 10. The OCTET4 field is a drop down of 254 values in a value set. I would like to have my users choose one of 254 values but only if it has not been used before. The problem I am having since I have multiple values that make up the first 3 fields are all of the values have been used. I would like to write a calculation where the 254 values in the value set for OCTET 4 is based off of the first 3 fields. Ex. 8.9.10. value set number 11 is free to use but 14.13.12. value set 11 is already being used therefore I cannot enter in the value of 11. Need Help.