code: private double convertStorageUnit(double value, StorageUnit sourceUnit,
  	                                  StorageUnit targetUnit) {
  		double byteValue = sourceUnit.toBytes(value);
  		return targetUnit.fromBytes(byteValue);
  	}
docs: convert the value from one storage unit to another.
  
  @param value - value
  @param sourceUnit - Source unit to convert from
  @param targetUnit - target unit.
  @return double.