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A crystal-controlled frequency standard having a frequency stability of a few parts in 1010 per day is described. The oscillator employs a 1-megacycle GT-cut crystal unit in a high-sensitivity bridge-balancing frequency-correction system. The crystal serves both as the resonant element for the oscilaltor and for a bridge whose unbalance is an indication of departure of the oscillator frequency from the crystal series resonance. The unbalance, greatly amplified, is used to AFC the oscillator.