Residual stress is commonly measured with X-ray diffraction and magnetic (magnetoelastic, micromagnetic) or Barkhausen noise techniques. The strain from the residual stress alters the atom spacing in a crystal. X-ray diffraction is useful in measuring the changes in atomic spacing. Barkhausen noise techniques are useful on ferromagnetic materials such as steels. Ferromagnetic materials consist of small magnetic regions resembling individual bar magnets called domains with each domain separated by a domain wall. Each domain is magnetized along a certain crystallographic easy direction of magnetization. Alternating magnetic fields will cause domain walls to move back and forth and result in an overall change in magnetization. An electrical pulse is induced by the magnetization in a micromagnetic probe or coil of conducting wire placed near the sample while the domain wall moves. The electrical pulses produced by all domain movements are added together to generate the noise-like signal called Barkhausen noise.