Add a sample to this measurements.

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)