# Plate Theory and Extensions - Column Efficiency > Page 55

Let the distance between the injection point and the peak maximum (the retention distance on the chromatogram) be (y) cm and the peak width at the points of inflexion be (x) cm. If a computer data acquisition and processing system is employed, then the equivalent retention times can be used.

Now, it has
already been shown that the retention volume of a solute is given by n(v_{m}
+ Kv_{s}), and twice the standard deviation of the peak at the
inflexion points is given by _{}

Thus, by simple proportion,

.

Then
_{ } (49)

Equation (49), can be used to calculate the efficiency of any solute peak from measurements taken directly from the chromatogram (or, if a computer system is used, from the respective retention times stored on disk). The measurement of column efficiency is a common method for monitoring the quality of the column during use.