[T.Matrix]

when I read fvMesh source code, I find that the cell volumes of old time and old-old time is dimensionedField. The code is as following. So why do they need to be set dimensionedField and don't set the same as Cell centres.

//- Cell volumes old time level
mutable DimensionedField<scalar, volMesh>* V0Ptr_;

//- Cell volumes old-old time level
mutable DimensionedField<scalar, volMesh>* V00Ptr_;