docs: def add_sample(self, ts, **kwargs):
          """Add a sample to this measurements."""
          if not self.series.offsets:
              self.ts = ts
              offset = 0
          else:
              dt = ts - self.ts
              offset = (dt.days * 24 * 60 * 60 * 1000 + dt.seconds * 1000 +
                        dt.microseconds // 1000)
          self.series.add_sample(offset, **kwargs)