13) Now you can refine which frames are stacked into the final image. Move the slider for the vertical red line and it will set a cutoff on the red quality curve. All frames that fall to the right of this red line, which corresponds to all images with a quality rating lower than 75% (see bottom of window), will not be used.
14) Next you can move the slider for the horizontal blue line and it will set a cutoff for the blue difference curve. All frames that fall above this blue line, which corresponds to all images with a difference rating greater than 47% (see bottom of window), will not be used.
15) You can look at the bottom to see how many frames are going to be included when stacked. There will be 341 frames stacked for this image based on the settings I've chosen. This indicates that 341 frames fall below the blue line and to the left of the red line.
16) Hit the Stack button and the selected frames will be stacked.