External cavity diode laser (ECDL) systems are presently experiencing a surge in popularity as laser light-sources, in Z 4:1 advanced optical communications- and measurement-applications. Because such systems require that their external reflectors be precisely controlled, to eliminate low frequency fluctuations (LFF) in optical output, we conducted experiments with a two-cavity version of the ECDL system. This technique brings the added advantages of a narrower linewidth than would be achievable via a single optical feedback. However, the ECDL's oscillation frequency is susceptible to the influences of the driving current, changes in the refractive index, and changes in external-reflector length that result from fluctuations in atmospheric temperature. We made every effort to maintain the length of the ECDL cavity, while evaluating oscillation-frequency stability. We used a Super-Invar board as the platform for our ECDL system, in order to minimize the influence of thermal expansion. Moreover, our ECDL system combines an Rb cell within an external cavity; an arrangement designed to improve stability by restricting the LD frequency within both the external cavity mode and the Rb-saturated absorption spectrum. We used the square root of the Allan variance, when evaluating oscillation frequency stability, observing, in the process, that it improved stability by about one order of magnitude.