This is used in EFT treatments to give the practitioner and the client a conscious awareness and way to know if there have been any changes in the feelings as the round progresses, and/or from one EFT treatment round to the other.

The SUE Scale - Subjective Units Of Experience

The SUD Scale Has Been Replaced By The SUE Scale Effective November 2011.

• Please note that the SUD scale ends with the "zero point of peace". In order to complete a full EFT treatment, one needs to go beyond that into POSITIVE emotions. See also Energized EFT.
  
• The possibility and the necessity to go beyond the zero point of feeling nothing is unique to energy work as the traditional psychology instrument of the SUD scale which was inherited from medicine/physiology stopped at 0.
  
• To bring about a "healing event" the opposite of the existing problem needs to come into being, and it does so reliably and easily when we improve the energy flow through the body.
  

A more complex version of the SUDs scale is the EI scale - scale of emotional intensity which goes from 100 - 0 and deals with multiple different emotions. See Advanced Patterns of EFT.

Since the onset of EMO, we use now the SUE scale instead of the SUDs scale.

SUE stands for "subjective units of experience" and goes from -10 (describing a trauma experience of the highest order) to +10 which describes an enlightenment experience or Guiding Star.

A lot of problems are due to conjunctions between trauma and Guiding star, so the SUE scale gives a better reading of what intense emotions are at play.

Further, as in energy work we are always improving the flow of energy, it is of the essence to go beyond "feeling nothing" and into the real energized end states which are on the positive wing of the SUE scale.

More information on the SUE scale:

http://eventspsychology.com/information/the_sue_scale_subjective_units_of_experience.htm

Using the SUE Scale to significantly enhance the practice of EFT Emotional Freedom Techniques is taught in the new EFT Master Practitioner Training and Energy EFT book by Silvia Hartmann.