What is a UK league?
A UK league was three miles, or about 4.828 kilometers. The length of a league varied between countries and centuries – three miles is the English figure.
The league has long since dropped out of use in Britain and survives mainly in fiction. Seven-league boots, at three miles a league, would cover 21 miles a step.
What is a chain?
The chain is a surveying unit of 66 feet, which is exactly 20.1168 meters. It is divided into 100 links of 7.92 inches each, and 80 chains make a mile.
The chain was devised by the English mathematician Edmund Gunter around 1620 and used to survey land. Ten square chains make exactly an acre, which is why surveyors liked it. GPS has replaced it for most work, though US public land surveys are still recorded in chains and links.