Cutting a quartz tuning fork crystal vibrator at a preferred angle and with a thickness which establishes a close coupled relationship between the flexural and torsional modes of vibration of the arms or tines produces a vibrator having a highly favorable cubic frequency temperature characteristic at...http://www.google.de/patents/US4320320?utm_source=gb-gplus-sharePatent US4320320 - Coupled mode tuning fork type quartz crystal vibrator
