Ephemeral devices

This is fascinating! A few GPS devices apparently had a mild(?) path offset issue few days ago:

The issue has to do with the ephemeris data file, also called the EPO file (Extended Prediction Orbit) or Connected Predictive Ephemeris (CPE). Or simply the satellite pre-cache file. That’s the file that’s delivered to your device on a frequent basis (usually every few days). This file is what makes your watch near-instantly find GPS satellites when you go outside. It’s basically a cheat-sheet of where the satellites are for the next few days, or up to a week or so.

I didn’t notice this on my Forerunner 235 but I find it super intriguing to read about the ‘inner workings’ of the background handshake. When I first got the Forerunner 235, I was amazed at how quickly it latched on to the satellites in contrast to the Forerunner 305 that I was actively using then.

A couple decades ago when you bought a new ‘gadget’, you would get not only a ‘how-to’ but also a technical sheet outlining the inner workings of the device. I miss seeing those sheets now!


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