assuming your data is stored in the vectors x1....x8 of the same length:
sum each component and divide by the number of lines:
x_mean=sum([x1,x2,x3,x4,x5,x6,x7,x8],2)./8
The plot in the plot:
plot(gca,time,x_mean);
if your time vectors are not the same then you will have to interpolate
