Dorper Guide cross bred percentages

Dorper Guide to cross bred percentages ( what does F1 F2 etc mean?)

F1 = ½ or 50%
F2 = ¾ or 75%
F3 = 7/8 or 87.5%
F4 = 15/16 or 93.75%
F5 = 31/32 or 96.88%
F6 = 63/64 or 98.84%