In the US Public Land Survey system, a section is supposed to be a square mile, but they never are that. Some are far more. Some are far less. Early surveyors (deputies of the surveyor general) hired to lay out the sections and quarter sections did so using compasses and followed cleared lines using wagons, counting the rotations of the wheels for measurements, or very heavy chains consisting of 100 8-inch links (66 feet). There are 80 chains in a mile.
A township contains 36 sections - the Northern and Western sections are where the error was intended to be, but we know all of the sections contain errors.
Anyway, those wheels wear down and perform differently over bumps. Chains stretch. Vertical difference posed problems.
This is why we have Professional Land Surveyors to retrace surveys.
