First, I applaud you effort and using side by sides when possible. But on your coin, the area SE id called split plating, not a RPM.
When making side by sides, I find determining the horizontal top line of the devices my first concern first. After determining this, them I crop both sets of image exactly the same. I usually make the widths the same. (I use a 1200 pixel width, making each image of the side by side 600 pixels wide. I add canvas on one image and set it for 1200 pixels by 1200 pixels square. I place the cropped images on to the canvas side by side. First thing I check is vertical alignment of the date. Tops of the devices of the dates should be not only the same width, but also the same height. I use underlines to match the different heights.
Note on this one, I labeled the line colors and also where I started each line as the source of height. When I find they are not a match, then I adjust the errant one to make them both the same height. Having this square first, helps to insure the mintmark locations are a match or not? On this one I placed images 1 then 2 on the top line and 2 then 1 on the second line. Why?
That is to show the horizontals are a match. Then the reverse order on the lower lines, to compare verticals to see if they match, or not. If not, they are probably not the same die number. Why the need to exact? Because on this year, Wexler lists over 350+ dies that he attributed. So finding an exact one takes a lot of work to attribute these. Sometimes I use more than one source die to see how the locations of the mintmark lines up. Seeing them side by side allows the perspectives not to go away from looking at to separate sources. I use this for doubled dies as well, but mostly for mintmark location matches. CoopHome
How to make SBS comparisons?