What's dual-frequency GPS and does my phone have it? Accuracy test on OnePlus 7 Pro vs S10+

A new term started creeping up in manufacturers' phone specs listing, making a cameo way back with the Xiaomi Mi 8 but still not as widespread as we'd like. Xiaomi even came out with the video you see above to brag about its virtues. 

The feature is marked in a specs sheet as dual-frequency GNSS (Global Navigation Satellite Systems), often ...