Thank you very much for your reply. I looked in the PPB menu but I wasn't sure how to enter the calibration value either. Positive or negative. I will try which one works. Congratulations on the great work on the Tinysa. I am aware of the difficulty of a project like Tinysa. I am working on an RF generator project and have achieved a maximum error or frequency accuracy of about 0.8 Hz. It is tremendously difficult. Thanks again
JCR