Simulation of black hole spin (using Eq. (9)) as a function black hole mass over various ranges of jet kinetic power. Coloured points represent estimated values from GRG observations. The solid curved lines with their respective colours indicate the different values of spin attainable by a black hole for a mass range of 10⁷ M_⊙ to 10⁹ M_⊙ at that particular jet kinetic power. The solid circles with different colours indicate the GRGs in our sample with their estimated spin values lying in the range of jet kinetic power specified. The total number of GRGs is 95. Figures mentioned in the square brackets in the legend of the plot indicate number of GRGs in respective kinetic jet power bins. The magnetic field used to compute the black hole spin (a) was assumed to be B_Edd, which is derived from the M_BH.