how to create a macro for some data processing

[Risa Ishida]

I’m beginner of Imagej and need to make a script, but I’m in trouble. I have one image data “A” as reference and each data “B”, more than 100 images, in a directory. I would like to find a total absolute difference value for all pixels between the A as reference and each data B in directory using the equation below. Could you tell me how to create a macro?

Σ{ | imageA - imageB | / imageA }
Both of A and B have same pixel size and same bit number.

Thank you in advance.
Risa