In the PBS Cross method, all possible combinations of conditions with one precipitant, one buffer, and one salt are generated using all of the precipitants, buffers and salts from multiple lead conditions (at their pHs and concentrations from the lead conditions), as shown in the image to the left.

PBS Cross optimization screens can be very useful in determining which components among several lead conditions are most important for crystallization.

In this example of a PBS Cross optimization screen, the lead conditions were Wizard™ #11, #17 and #18.  Among these three different conditions are three different precipitants (blue hues), three different buffers (red hues), and two different salts (green hues).  The total number of different combinations of conditions with one precipitant, one buffer and one salt in each condition is
3x3x2 = 18.  Additional precipitants, buffers and salts can be added to increase the combinatorial diversity of the optimization area.