The original GLF23 model described in the 1996 Waltz paper  uses the flux-surface-averaged shear rate in circular geometry with a multiplier of . Here, vE is the shear velocity equal to . Since then it was discovered that the rate can often exceed the maximum linear growth rate in the outer half of the plasma leading to the formation of an unphysical transport barrier. This was remedied by using a real geometry extension of where the toroidal field in vE is replaced by . Here, the factor typically rises to 2-3 in the outer half of elongated plasmas, thus reducing the rate in that region significantly. The corresponding multiplier for the original (retuned) models is which has been found to be consistent with recent gyro-kinetic simulations by Waltz. To use the real geometry shear, set bt_flag=1 in the namelist input. The effective B-field is computed internally in subroutine callglf2d.f.