I'm having issues with the flatness of the Synchronous AC on a 3458A that I'm calibrating. The 1V range at about 1Khz has a sharp rise in value, and it reads out of tolerance at that point, but all the other frequencies on that range are good. I looked into the adjustment procedure, and found an AC flatness adjustment, and performed it, but it only adjusted the high frequency flatness and gain; The low frequancies were still not flat. Is there a low frequency adjustment for this?