A knotted cord was a primitive surveyor's tool for measuring distances. It is literally a length of cord with knots at regular intervals. They were eventually replaced by surveyor's chains, which being made of metal were less prone to stretching and thus were more accurate and consistent.
Knotted cords were used by many ancient cultures. The Greek schoenus is referred to as a rope used to measure land. Ropes generally became cables and chains with Pythagoras making the Greek agros a chain of 10 stadia equal to a nautical mile c 540 BC. The Romans used a waxed cord for measuring distances.
An interesting form of a knotted cord is one 12 lengths long (the units do not matter) which is closed into a loop. This cord can be used to lay out a right angle by forming the loop of cord into a 3–4–5 triangle. This could be used for laying out the corner of a field or a building foundation, for instance.
Knotted cords were used by rope stretchers, royal surveyors who measured out the sides of fields (Egyptian 3ht). The knotted cords (Egyptian ht) were 100 royal cubits in length with a knot every hayt or 10 royal cubits. The rope stretchers stretched the rope in order to take the sag out it and keep the measures uniform.
Since land in Egypt was measured in several different units there would have been knotted cords with the knots spaced in each unit including mh t3 or land cubits, remen royal cubits, rods or ha3t, generally the lengths in multiples of 100 units. The longest measured length listed in the Rhind papyrus is a circumference of about a Roman mile with a diameter of 9 khet.