mixed rank range values

Hi,

Is it better to return the following VisAD MathType:

    (FunctionType (Real): (time) -> (lat, lon), FunctionType:
    (time) -> FunctionType (Real): (altitude) -> (pressure, temperature))

which is a Tuple of two, separate Fields -- or this, equivalent, one:

    (FunctionType (Real): (time) -> (lat, lon, 
    FunctionType (Real): (altitude) -> (pressure, temperature)))

which is a Field with a Tuple range comprising two Scalars and a Field?

--Steve