This method determines the elongation of fabrics, yarns, threads and cords between two limits of force on a tensile testing machine.

The elongation of a specimen between any two forces is determined from the measurement, at each of these forces, of the distance between two reference marks on the specimen.

The difference in clamp-separation between two specified forces is commonly used as a measure of elongation, but such values will be greater than the true elongation if there is flow of the specimen out of the proximal edges of the clamps as the force increases. Where the amount of flow-out from jaw-type clamps is small in proportion to the true elongation, it is frequently ignored, and the elongation value obtained by measurement of clamp-separation in such cases is designated "apparent elongation". Where the flow-out is relatively large, its approximate amount at the specified forces may be measured and applied as a correction. (The presence or absence of flow-out and its amount depends on the type of textile material, the construction of the clamps, and the distribution of the clamping pressure over the clamped areas of the specimen. Flow-out must not be confused with slippage of the specimen in the clamps, which is indicated by movement of its free ends.) The separation of drum-type clamps cannot be used for the determination of specimen elongation and reference marks must be placed on the specimen.