The Hallade method, devised by Frenchman Emile Hallade, is a method used in track geometry for surveying, designing and setting out curves in railway track. It involves measuring the offset of a string line from the outside of a curve at the central point of a chord. In reality, string is too thick to provide a clear reading and breaks easily under the tension needed to minimise movement due to wind. A reel of wire may be used instead, with special holders (Hallade forks) employed to hold the wire at a fixed distance from the rail. The measurement is taken with a Hallade rule, a specialist ruler whose zero point matches the offset of the forks, thus cancelling it out. The purpose of the offset is to allow small negative measurements. Without this, surveyors would frequently have to read fr