I'm building an app to save data and some calculations made with those datas, the idea is keep the data in one model and the calculations in other. So, the models are like this:

class FreshData(models.Model):
    name = models.CharField(max_length=20)
    one = models.IntegerField()
    two = models.IntegerField()

    def save(self, *args, **kwargs):
        Calculations()
        Calculations.three = self.one + self.two
        super(FreshData, self).save(*args, **kwargs)
        Calculations.save()

class Calculations(FreshData):
    three = models.IntegerField()

I've got a valueerror pointing out "self.one" and "self.two" as without value. I keep the idea in witch my design is wrong and django has a simpler way to store related data.