Digits for each technology are stored separately.
The container for each technology is a Ma/Meesen IdentifiableContainer,
I.e. a collection of subcontainers.
Each subcontainer holds all the digits from one ROD (readout driver).
(A ROD contains data from multiple chambers.)
Raw data can be unpacked at this same granularity.
If digits are
extracted from a subset of the ROD's, then only those ROD's are unpacked.
Our user interface should not expose this implementation.
We can later
change the granularity of the persistent storage and unpacking without
changing the user interface.