A mathematically-constructed diagram used to check for coincidences of vibration sources (1', 2', etc., shaft speed) with rotor natural frequencies, which result in rotor resonances. It plots frequency vs. RPM. Plot size grows with increasing amplitude. Synonymous with interference diagram.
Tip excerpted from: The Professional's Guide to Maintenance and Reliability Terminology by Ramesh Gulati, Jerry Kahn and Robert Baldwin
