Commercial Cesium Beam Primary Frequency Standards

HP 5061A and 5061B primary frequency standards (cesium)

HP 5062C primary frequency standard (cesium), HP 5065A secondary frequency standard (rubidium)

FTS 4050 primary frequency standard (cesium)

Hewlett-Packard flying atomic clock era (Len Cutler with hp 5060 cesium)

HP 5062B PFU Precision Frequency Unit for collision avoidance