To measure longitude, what should be the reference point for the dividers?

The reference point for the dividers when measuring longitude should be nearest the object. This approach allows for precise measurement relative to the actual position of the object being navigated. By placing one leg of the dividers at the object's position, the measurement taken can reflect the direct distance to the desired longitude line, ensuring accuracy in navigation.

Other reference points, such as the north pole, equator, and Tropic of Cancer, do not provide the necessary context for various object locations on a chart. Measuring from nearest the object is essential for effective navigation, particularly in avoiding errors that could arise from fixed reference points that may be far removed from the object's actual position.