Fisher Scientific Accumet Basic AB30 User Manual page 38

ÒsiemenÓ. Conductivity measurements are reported as Siemens/
cm, since the value is measured between opposite faces of a cell
of a known cubic configuration. With most aqueous solutions,
conductivity quantities are most frequently measured in
microSiemens per cm (µS/ cm) or milli-Siemens per cm (mS/ cm).
The accumet Basic AB30 meter automatically converts conductivity
readings from micro or milli Siemens to other derived units that are
widely used. These are ppm TDS (total dissolved solids), and
Resistivity (ohm*cm).
Some users prefer the use of Resistivity units to describe their
water, particularly where high purity water is involved. The unit
most often used to describe Resistivity is megohm*cm, which is
simply the reciprocal of conductivity (µS/ cm). The chart below
shows the relationship between these units.