I like to know what the local and UTC time is when I’m at my HAM equipment. I had two clocks hanging on the wall. One 24 hour clock for UTC and another 12 hour clock for local time. The 24 hour clock was “Atomic” which means it was suppose to synchronize once every 12 hours from WWV. In our house my shack was relegated to the lower level of our house. The “Atomic” clock never had sufficient RF signal to synchronize and of course there is no external antenna connection. It seemed like I was always taking the clocks off the wall, correcting the time and putting them back up on the wall. One day I was playing with an app on my smart phone that displayed the number of visible GPS satellites and I noticed that at least 3 were available most of the time. Armed with this information I set out to build a clock that displayed UTC and local time and was kept accurate using the GPS satellite constellation.