To calcuate % difference and error of two plots obtained?

true=multibandread('paris.lan',[512,512,7],'uint8=>uint8',128,'bil','ieee-le');
Nof_bands=7;
for k=1:Nof_bands
t_value=true(:,:,k);

          x(k)=double(t_value(38,333));
          y(k)=double(t_value(38,334));
          z(k)=double(t_value(39,333));
          b(k)=double(t_value(39,334));
          x1(k)=double(t_value(486,115));
         y1(k)=double(t_value(486,116));
         z1(k)=double(t_value(487,115));
         b1(k)=double(t_value(487,116));
         avg(k)=double(x(k)+y(k)+z(k)+b(k))/4;
      avg1(k)=double(x1(k)+y1(k)+z1(k)+b1(k))/4;

end
d=[1:1:7];
figure(1)
plot(d,avg,'r',d,avg1,'g');

[Guillaume]

I do not see a question anywhere, just some code with no comments. Are we supposed to guess what you want?

Note that naming your variable true (or false) is an extremely bad idea.