[CF-metadata] COARDS name for a time offset

[John Caron]

ok, let me try this again:

abstractly, we have swath data with 2D time coordinates.
since the swath data occurs at the same lat/lon pixels, it is useful to 
make these into 3D variables:

   variable[t, y, x]
     
which have coordinates:
   lat[y,x]
   lon[y,x]
   time_for_variable[t,y,x]

the times for different variables may be different.

to save space, we want to calculate the time variables, instead of 
storing them,  as:

  time_for_variable[t, y, x] =  reference_time[t] + sst_dtime[t,y,x] + 
time_offset_for_variable

or is it

  time_for_variable[t, y, x] =  reference_time[t] + sst_dtime[t,y,x] + 
time_offset_for_variable[y,x]

as jonathan suggests??

does this capture the issue correctly?

if so, and we want to proceed, perhaps a "formula" attribute (a la 
grid_mapping)  would be a good generalized way to do these calculations?