For anyone wondering, MAC = Miniature Atomic Clock. From the vendor product page:
> Microchip’s next-generation MAC-SA5X miniaturized rubidium atomic clock produces a stable time and frequency reference that maintains a high degree of synchronization to a reference clock, such as a GNSS-derived signal, despite static g-forces or other factors. Its combination of low monthly drift rate, short-term stability and stability during temperature changes allow the device to maintain precise frequency and timing requirements during extended periods of holdover during GNSS outages or for applications where large rack-mount clocks are not possible.
* https://www.microsemi.com/product-directory/embedded-clocks-...
Article by some folks from the manufacturer giving details on the capabilities (with graphs and such):
* https://www.gpsworld.com/new-miniature-atomic-clock-aids-pos...
Generally: if accurate positioning, navigation, and timing (PNT)—especially timing—is important in your infrastructure, then you need to plan for GNSS outages.
> In the event of the GNSS signal loss, we need to make sure the time drift (aka holdover) of the atomic-backed Time Card stays within 1 microsecond per 24 hours. Here is a graph showing the holdover of the atomic clock (SA.53s) over a 24-hour interval. As you can see, the PPS drift stays within 300 nanoseconds, which is within the atomic clock spec.
* Article.