[Fixed]-Django: is it possible to keep a model field updated with a model method?

As Daniel Roseman pointed out, you can override save method on Calibration model. For example:

class Calibration(model.Model):
    # your fields

    def save(self, *args, **kwargs):
        super(Calibration, self).save(*args, **kwargs)

        # update latest calibration date 

You can store your parameter in many ways, for example by creating Parameter model for storing your variables.

class Parameter(models.Model):
    key = models.CharField(max_length=255, unique=True)
    value = models.IntegerField()
    description = models.TextField(blank=True, null=True)

    def __str__(self):
        return self.key

and then again in save:

import time

p = Parameter.objects.get(key='LATEST_CALIBRATION_DATE')
p.value = time.time() # save in UNIX timestamp
p.save()

or whatever format you like.