Harrison, aided by his brother, measured the accuracy of his timepiece over many nights by marking the precise moment when certain stars disappeared from his view behind a neighbor’s chimney.
Dengan bantuan adiknya, Harrison selama bermalam - malam menghitung keakuratan jam buatannya dengan menandai kapan persisnya bintang - bintang tertentu menghilang dari pandangannya di balik cerobong asap tetangga.