pressure gradient correction factor in gas chromatography

A factor that corrects for the compressibility of the carrier gas. The values of the measured quantities obtained after multiplication by the factor $j$ are independent of the pressure drop in the column. If $p i$ , $p o$ are respectively the pressures of the carrier gas at the inlet and outlet of the column, then $j$ is given by:

$j = 3 [ ( p i p o ) 2 − 1 ] 2 [ ( p i p o ) 3 − 1 ]$

Source:

Orange Book, p. 101