In general, when there is background conductivity, the conductivity
versus concentration curve will not be the same as the standard
curve for caustic (NaOH) in distilled water, due to buildup of salts
in the bath. The curve must be developed from operating data, i.e.
conductivity and titrated caustic concentrations. Data should be
taken over the life of at least three (3) baths; the age of the bath
and any additions to the bath should be noted, in addition to the
conductivity and titrated caustic concentration. Once a curve has
been developed, the on-line measurement can usually be corrected
for salt build-up by standardization following a routine laboratory
titration.