The Efratom Model M-100 Rubidium Frequency Standard (RFS), Part Number (P/N) 70502-1, is a sub-compact, lightweight, atomic resonance-controlled oscillator. The unit provides a pure and stable 10 MHz sinusoidal signal from a 10 MHz voltage-controlled crystal oscillator (VCXO), which is referenced and locked to the hyperfine transition of Rubidium 87 (Rb 87). The reference element is an optically-pumped integrated rubidium vapor cell, contained within the physics package. For the standard M-100, this technique provides long-term stability of ≤ 6x10-11/month (≤ 3.6x10-10 for first year) improving to ≤2x10-10/yr starting with the second year. The M-100 was designed to be used by the military as a Master oscillator in high-performance communication systems, frequency standard equipment, advanced navigation equipment, and all other systems which require extremely precise frequencies and time intervals. With the proper input power provided and suitable cooling provisions, the M-100 can be used as a free-standing secondary frequency standard for laboratory and testing purposes.