The best tool to measure a football field is a yard stick. AnswerParty
Tools are used by some animals to perform behaviours including the acquisition of food and water, grooming, defence, recreation or construction. Originally thought to be a skill only possessed by humans, some tool use requires a sophisticated level of cognition. There is considerable discussion about the definition of what constitutes a tool and therefore which behaviours can be considered as true examples of tool use. A wide range of animals is considered to use tools including mammals, birds, fish, cephalopods and insects.
Rarely, animals have been observed making their own tools, e.g. primates removing leaves and twigs from a branch or sharpening a stick to use as a weapon.
Magnetic flux leakage (MFL) is a magnetic method of nondestructive testing that is used to detect corrosion and pitting in steel structures, most commonly pipelines and storage tanks. The basic principle is that a powerful magnet is used to magnetize the steel. At areas where there is corrosion or missing metal, the magnetic field "leaks" from the steel. In an MFL tool, a magnetic detector is placed between the poles of the magnet to detect the leakage field. Analysts interpret the chart recording of the leakage field to identify damaged areas and hopefully to estimate the depth of metal loss. This article currently focuses mainly on the pipeline application of MFL, but links to tank floor examination are provided at the end.