Just as people experience physical pain differently, so too do people experience emotional pain differently.   Relative physical pain indexes are now proven enough to show that different people feel physical pain very differently. 

Neurotechnoloy will enable a similiar relative understanding of individual differences in mental health.  A Relative Emotional Gauge (REG) would help people better empathize with each other or understand the depth of their depression or height of their joy relative to other people's experiences.

So how happy are you today?  I'm an 8!