Apollo-era rubidium calibration clock likely used by NASA to calibrate timing reference sources, measuring approximately 7.5 x 7 x 17.5 , featuring a 24-hour Patek Philippe face surrounded by a large second-dial, "Loop Null" and "Battery Current" indicators below, a fine-tuning knob, and multiple switches. Inputs for multiple frequencies line the top of the unit. A NASA/Goddard Space Flight Center" property label is affixed above the clock face, the right side has an affixed manufacturer's label, "Model 307A Rubidium Clock, General Technology Corporation, Los Angeles, California, Subsidiary of Tracor, Inc." The top has a tag with a date of "8-72," and the rear provides access to the AC input and fuses. The power cord is included. In very good to fine condition.
The rubidium standard is used to provide a very stable timing reference source; this was more prevalent prior to the availability of GPS timing. A portable time and frequency standard is essential for 'range' applications. For example, making sure that the time setting of the various cameras used to film (or video record) launches was the same so that the timing of events captured on film could be synchronized. The portable rubidium clock would be set from a master clock (referenced either to a local atomic clock or the time standards of the Naval Observatory or National Institute of Standards and Technology) and carried to the locations that did not have access to a direct time reference. Currently, this could be done using a GPS receiver for time distribution, but in the era when this clock was used it was more convenient than existing time distribution methods (short wave radio, very Low Frequency radio and some navigation systems). The clock/frequency standard contains the rubidium oscillator and uses a Patek-Philippe time display register (it is not a clock on its own, it uses pulses from the oscillator to run the mechanism of the display). It originally housed a battery pack, which was removed to avoid damage from battery corrosion.
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