Longitude is best determined experimentally by?

Answer 1

... a licensed land surveyor or a trained navigator.

Answer 2

using instruments such as a sextant or a GPS device. These instruments help in measuring the angle between a celestial object (like the sun or a star) and the observer's location on Earth. By comparing this measured angle with the known angle of the celestial object at a reference location, the longitudinal difference can be calculated. Additionally, using a GPS device can provide accurate longitude readings by receiving signals from satellites in orbit.