cartography - Declination Diagram

1. 
   

   What point on a UTM map does the declination diagram refer to? Is it the centre? Is it the edges? Is there a standard?

   
   


2. 
   
   

   The central meridian on a UTM map points to true north. Are grid north and true north arrows identical only at this central meridian? If they are identical then what point on the UTM map does the grid north arrow on the declination diagram refer to?

   
   


3. 
   

   If all grid lines on a UTM map point to true north (causing increased distortion with distance from the central meridian) then why is there a convergence angle (grid north to true north) on the declination diagram?