In practical terms, the cell constant (K value) refers to the distance between the electrodes within the sensor, with a lower number meaning a smaller distance. It is calculated by dividing the area (a) normal to the current flow squared by the distance (d) between the electrodes. Low K value sensors are used in lower conductivity solutions, where the smaller distance raises the conductance allowing for easier measurement. The opposite is true in high conductivity solutions, where a larger K value may be more suitable. Pi sensors are available in K values of 0.1, 1 and 10.