How to shift my data in Y direction ?

How I can shift the red coloerd data or the black coloerd data in the image below thus both are starting at same points in the y dierction so I will be able to compare the data?

Any suggestion? Please!!!

[Walter Roberson]

http://www.mathworks.co.uk/matlabcentral/answers/43073-a-guide-to-tags

[Walter Roberson]

minred = min(red_data);
minblack = min(black_data);
base = min(minred, minblack);
plot(time, red_data - base, 'r', time, black_data - base, 'k')