Righting moments are measured in foot-tons. Since
the righting arm (GZ) is equal to GM times sin θ, for
small values of θ, you can say that the righting
moment is equal to W times GM times sin θ. Because
of the relationship between righting arms and righting
moments, it is obvious that stability may be expressed
either in terms of GZ or in righting moments.
However, you must be very careful not to confuse
righting arms with righting moments; they are NOT
identical.