When just a crystal is needed, one of the smallest is the CX18 crystal from Statek Corp., at just 1.55 x 0.95 x 0.35 mm. The surface-mount crystal is available for frequencies of 30 MHz and higher, with samples of the 50-MHz device currently available. The miniature crystal, which weighs typically 1.8 mg, offers calibration tolerances in the range of 5 PPM. It is available with a glass lid and is suitable for medical, industrial, and military applications.