A more thorough explanation:

Chancellor's foot is a term used to describe the variability of equitable justice. It means that the fairness of a decision depends on the conscience of the Chancellor, who is the judge. The phrase was coined by John Selden, a 17th-century jurist.

For example, if two people have a dispute and go to court, the judge may use equitable justice to make a decision. However, the decision may not be the same if a different judge, who has a different conscience, hears the case. This is because the Chancellor's foot is an uncertain measure, just like the length of a person's foot can vary.

In other words, the Chancellor's foot symbolizes the subjectivity of equitable justice and how it can vary from judge to judge.