This crossplot is used to determine clay bound water (CBW) resistivity. Generally CBW has an equivalent NaCl salinity between 3,000 ppm and 5,000 ppm, with 4,000 ppm being the most common value (see the reference below).
Start by inputting resistivity-VCBW data series (green, blue and orange cells). Each data series allows an unlimited number of rows, and cut and paste functionality is available. Next, adjust CBW resistivity until the CBW line fits the desired data series. Although slope (m) can be adjusted, it should generally equal 1.00 (acts like a fracture in an Archie rock). Once you have a match, record the CBW resistivity value for petrophysical analysis work. Also note the temperature the resistivity data were acquired (wellbore temperature), so that the CBW resistivity value can be temperature corrected to a standard reference temperature (25 deg. C or 77 deg. F).
The theory behind this crossplot is based on Dick Merkel's presntation titled Electrical Properties of Clays. The presentation was put together for SPWLA's Nuggets of Wisdom video series and can be viewed using SPWLA's member portal.