An excellent article about Frequency calibration using WSJT-X: (From the WSJT-X Group Thread) https://drive.google.com/file/d/1TDmsfPBzw7poLVA-G6JNWdXn4qJgeY93/view or https://drive.google.com/open?id=1TDmsfPBzw7poLVA-G6JNWdXn4qJgeY93