What does "undersap" measurements mean? What is a "stow" factor?

Question

The questions come from the following sentence: "You advised that weight is 9000 tons and 10000 cubes, that means that the stow factor is1:1,or is freight based on undersap measurements then we need the stow factor."

Answer 1

The stowage factor of a cargo is the ratio of weight to stowage space required under normal conditions. It indicates how many cubic meters one metric ton of a particular type of cargo occupies in a hold, taking account of unavoidable stowage losses in the means of transport or the CTU (Cargo Transport Unit).
undersap is not a word
:)