This page explains the various caveats of positioning and orientation of the various component images within merge. The help file within merge does not include this page.Scroll methods for source 1,2 and the target
Source images can be generated from a file, pasted from the clip board, pasted or written text, or software generated pattern. Either source when present can be over written at any time by one of the methods above. Irrespective of where they originated, each source (but not the target) can be positioned, rotated and scaled independently of the other source.
Merge must make a decision when a source image is replaced with another without the user explicitly changing the rotation and scaling settings of that source. It can leave the settings as is or automatically reset them to zero degrees rotation, default scaling and positioning. There are many cases where there is a need to try various images with the same orientation and size against a "fixed" image.
It has been decided in merge to leave settings unchanged when changing images to the same type such as file image to another file image. Rotation, scaling and positioning will only be reset to their default values when an image changes to another type.Examples of change to an image include: pasted image to text; file image to software generated pattern etc.