Seismic magnitude scales indirectly and incompletely reflect the force of an earthquake, involve other factors, and are generally limited in some respect of magnitude, focal depth, or distance. The "moment magnitude scale" – Mw or M – developed by and , is based on an earthquake's "seismic moment", M, a measure of how much work an earthquake does in sliding one patch of rock past another patch of rock. Seismic moment is measured in Newton-meters (Nm or Nm) in the SI system of measurement, or dyne-centimeters (dyn-cm) in the older CGS system. In the simplest case the moment can be calculated knowing only
Apparent magnitude further qualification, it is usually the V magnitude that is meant, more or less the same as visual magnitude. Because cooler stars, such as red giants and red dwarfs, emit little energy in the blue and UV regions of the spectrum their power is often under-represented by the UBV scale. Indeed, some L and T class stars have an estimated magnitude of well over 100, because they emit extremely little visible light, but are strongest in infrared. Measures of magnitude need cautious treatment and it is extremely important to measure like with like. On early 20th century and older orthochromatic