I often read that the k-meta contain 57% sulphite and the campden
tablets 48%. I would like a clarification on that.

A) Is the 57% mean the % of sulphite contain in a given amount of
k-meta from wich you will get some bound SO2 and free SO2

OR

B) The 57% mean that from any given amount of k-meta added you will
roughly get 57% of free SO2 ( theorical of course )

Thanks for your explanations

Séb