There is an intriguing digital GPS clock atTindie.com/products/nsayer/gps-clock/ Made by Geppetto Electronics <https://www.tindie.com/stores/nsayer/>, it receives and displays GPS time and claims 200 us accuracy. Put this clock next to a common AC-powered digital clock and watch the difference wander around over days and weeks.It's not time-nuts precision, but it is interesting. Doug Hutton, W5JUV Lubbock