How can I define reference area in SNAP

[Shadi1]

@ABraun

If an area with no change has 15 mms in the relative displacement, you can make all pixels 15 units smaller and have the absolute displacement.

@ABraun

They show the relative displacement with respect to the primary image (depending on the date).
SNAP cannot know the actual (absolute) displacement

So the master date1 was considered the date when the displacement has initiated?
meaning that all pixels of the secondary image at date2 represent targets that have moved away or towards the sensor starting from their zero position during date 1? Then how come such relative displacement be false?