[QUANTITY] Why quantities always have errors

[Mark Cresitello-Dittmar]

Hi,

Brian.. in your model, is ERROR required to have the same
dimensionality,units,Frames as the Value it is associated with?

If it does, I don't think I like it.
If it doesn't then it is in itself a QUANTITY cuz it has
  dimensionality, units, frames, etc..
If error it is a quantity, then it would have an error? (ExactNoError?)

My current thinking for our model is to define a thing which has:
   + Axis Frames (with Mappings between)  <- defines data axes
   + Value Frames (with Mappings between) <- defines Units etc.
   + Dimensionality/data_type etc.        <- provides access to 'values'

This would be my 'Quantity', if I want to associate an error with this
thing I could:
   A) Make a quantity which is a vector of 2 quantities  1=value 2=error
   B) Define a 'measurement' which has two quantities, a value and
        associated error, and probably some other stuff...

Two non-exclusive means of obtaining the same goal without requiring
every 'value' to have an error, and allowing a lot of flexibility in
defining the error since it doesn't need to have the same structure as
the 'value' it is associated with.  One could have an error which is
a vector of several 'flavors' of error (systematic, efficiency,...)

Mark