Open-sourcing a more precise time appliance

I didn’t want to click this so I assume others here won’t either. Here’s the top points they highlight themselves:

- Facebook engineers have built and open-sourced an Open Compute Time Appliance, an important component of the modern timing infrastructure.

- To make this possible, we came up with the Time Card — a PCI Express (PCIe) card that can turn almost any commodity server into a time appliance.

- With the help of the OCP community, we established the Open Compute Time Appliance Project [1] and open-sourced every aspect of the Open Time Server.[2]

1. https://www.opencompute.org/projects/time-appliances-project...

2. https://github.com/opencomputeproject/Time-Appliance-Project...

I'm still unclear why they need the MAC on top of the GNSS reception. I can understand if it's just to provide holdover in event of GNSS signal loss, but they seem to be saying that it provides better precision when you've got both.

Off topic: I'm reminded of a very small unit of time that was devised to be a least common multiple of various division of time like 24fps, 30fps, 44.1kHz, and a ton of others in video and audio. Does anyone remember what this unit was?

If I read correctly:

GNSS PPS is more jittery but does not drift. The MAC has 1000x less jitter but drifts. You can cleverly combine them with statistics and magic to get the best of both worlds.