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 ]
Orange Book, p. 101