def measureSize(self, diffTo, diffFrom, estimatedSize, chunkSize, isInteractive):
        """ Spend some time to get an accurate size. """
        diff = self.toObj.diff(diffTo, diffFrom, estimatedSize)
        isInteractive = self.toObj.bool(isInteractive)
        self.butterStore.showProgress = None if isInteractive else False
        self.butterStore.measureSize(diff, int(chunkSize))
        return self.toDict.diff(diff)