Microsecond accurate NTP with a Raspberry Pi and PPS GPS - Austin's Nerdy Things
Adafruit Ultimate GPS HAT for Raspberry Pi A+/B+/Pi 2/3/Pi 4 [Mini Kit] : ID 2324 : $29.95 : Adafruit Industries, Unique & fun DIY electronics and kits
Adafruit Ultimate GPS | Technology Tutorials
Amazon.com: C4Labs Zebra Case Kit for Adafruit GPS HAT and Raspberry Pi 4B 3B, 3B+, and Pi 2B : Electronics