@ https://superuser.com/questions/290656/combine-multiple-images-using-imagemagick
Reading these posts I was able to join images vertically, however if you see the result ..bottom image needs a slight pixel offset (because its y-axis is 2-figure value as compared to upper image having y-axis of 3-figure, x-axis is same & at constant interval)
If I can just give bottom picture a slight nudge to the right, x-axis will appear more appropriate