~~ If log1227 = a, then log616 is:
log616=log1216/log126
=2log124/1/2log1236
=4log1212/3/log1212*3
=4(1-log123)/(1+log123)
=4(1-a/3)/(1+a/3)
=4(3-a/3+a)
=2log124/1/2log1236
=4log1212/3/log1212*3
=4(1-log123)/(1+log123)
=4(1-a/3)/(1+a/3)
=4(3-a/3+a)