Standard Absolute Activity
The "Standard Absolute Activity" is proportional to the absoulte activity of the pure substance $B$ at the same temperature and pressure multiplied by the standard pressure.
Applicable units are those of quantitykind:StandardAbsoluteActivity
http://en.wikipedia.org/wiki/Activity_coefficient
$\lambda_B^\Theta = \lambda_B^*(p^\Theta)$, where $\lambda_B^\Theta$ the absolute activity of the pure substance $B$ at the same temperature and pressure, and $p^\Theta$ is standard pressure.
http://www.iso.org/iso/catalogue_detail?csnumber=31894