This was not as strange as it sounds, for Halley had been working on determining the longitude using variation of the compass and this was the main purpose of the voyage, although he was also required by William III to:
Ito ay hindi na kakaiba ito bilang mga tunog, para sa Halley had been nagtatrabaho sa pagtukoy ng longitude na gumagamit ng pagkakaiba-iba ng kumpas at ito ay ang mga pangunahing layunin ng paglalakbay, kahit na siya ay kinakailangan din sa pamamagitan ng William III sa: