How many stereoisomers does nona-2,3,5,7-tetraene, $\mathrm{CH}{}_3-\mathrm{CH}=\mathrm{C}=\mathrm{CH}-\mathrm{CH}=\mathrm{CH}-\mathrm{CH}=\mathrm{CH}-\mathrm{CH}{}_3$, have? Count enantiomers separately.

Identify the stereogenic units. The allene unit C2=C3=C4 has $\mathrm{H}$/$\mathrm{CH}{}_3$ on one end and $\mathrm{H}$/alkenyl on the other, so it is an axis of chirality (2 forms). C5=C6 and C7=C8 are each stereogenic double bonds ($E$ or $Z$). The molecule has no symmetry, so the units are independent: $2\times 2\times 2=8$.