Yes, that's correct, thanks for pointing this out! I added a note in the article for this as well to make it clearer. This GPSWorld article does a pretty good job of explaining the differences between NAD83 and WGS84 - https://www.gpsworld.com/data-collection-of-wgs-84-information-or-is-it/. In short you should convert from NAD83 to WGS84 before entering coordinates in GPSTest or you'll likely have several additional meters of error.