A subcube is a construct that HFM uses to cache data in memory. A subcube is defined by the combination of one member from each of Scenario, Year, Entity and Value and contains every single data cell defined by all possible combinations of the rest of the dimensions. That is why it is called a subcube, it is a cube defined by all possible combinations of Account, ICP, Custom1-4 for a fixed Scenario, Year, Entity and Value combination. You will ask: where is the period here? The answer is that a subcube comes in as a set of records, each record containing a unique Account, ICP, Custom1-4 combination with 12 values (provided that you have defined a month as a period).