Émile and Odette Thellier were the first to make laboratory measurements to determine the strength of the ancient field responsible for producing remanent magnetization in a rock or archeological artifacts.
[1] Absolute paleointensity determinations involve measurements that attempt to quantify the past field strength that produced a magnetization in a rock or other material that has cooled from a high temperature.
Most of these methods involve progressively removing the natural remanent magnetization (NRM) by thermal demagnetization and replacing it with a laboratory thermoremanent magnetization given in a magnetic field of known strength and direction.
[2] Various methods for measuring absolute paleointensity include: Relative paleointensity determinations are often used in materials that may be destroyed or strongly altered during heating, such as lake and marine sediments.
[6] A measure of relative changes in paleointensity may be obtained by normalizing the NRM by a factor that represents the concentration of magnetic grains in a sample, such as the anhysteretic remanent magnetization.