The 660 is
the QNH/1013 correction...so we need 10600 + 1500 - 660 = 11440ft...now correct
for temp (ISA -15)...4%/10 degrees, ie 6%...from ac to datum (SL).....6%x11440
= 685ft...now, high to lo careful go...so it is a plus
correction...11440 + 685 = 12125ft.....we need an EVEN level....FL140