Precision – Allan Variance (two sample variance)

The quality of data / stability of an instrument is characterized by the accuracy (shift from true value) and the precision (statistical distribution of values and drift due to external influence). A good measure is the Allan variance/Allan deviation which chops the time course of data into equaliy spaced intervals τ and compares these intervals, generating the Allan variance σ:

Simulated data

    Signal noise in ppm
  • 13CO2 = 0.1
  • 12CO2 = 1
    Signal drift (linear) in ppm
  • 13CO2 = 0.1
  • 12CO2 = 2