For use with Keysight model and serial numbers: Model 6571A: US36520101 and Above Model 6572A: US36350101 and Above Model 6573A: US36330101 and Above Model 6574A: US36340101 and Above Model 6575A: US36340101 and Above Model 6671A: US36400101 and Above Model 6672A: US36390101 and Above Model 6673A: US36380101 and Above Model 6674A: US36370101 and Above Model 6675A: US36370101 and Above