Giddings [16] proposed the function () to define the resolving power (R) of a column. This function is analogous to a very similar expression used in spectroscopy to define spectroscopic resolution, i.e., (), where (Dl) is the minimum wavelength increment that can be resolved at a mean wavelength (l). The value  that would be analogous to (Dl) in spectroscopy was (Dk'), the band width at the base of the eluted peak. Consequently, (Dk') will be equivalent to twice the peak width at the points of inflexion or four times the standard deviation (4s). From the plate theory, (R_r) the concept of resolution as introduced by Giddings, will be given by

Dividing through by (v_m ), and noting that , 

                                                           (58)

Equation (58) shows that the resolving power as defined by Giddings is directly proportional to the square root of (N_E), the number of effective plates. Thus, (R_r) can also be used to compare the resolving power of different columns of any size or type. However, the magnitude of (R_r) will still depend on the (k') of the solute used for measurement and thus comparison between columns must be made using data for solutes that have the same, or very similar, (k') values.