modified version of Allan variance, measurement of frequency stability in clocks, oscillators and amplifiers
![{\displaystyle \operatorname {mod} \sigma _{y}^{2}(n\tau _{0})={\frac {1}{2\tau ^{2}}}\left\langle \left[{\frac {1}{n}}\sum _{i=0}^{n-1}x_{i+2n}-2x_{i+n}+x_{i}\right]^{2}\right\rangle }](https://wikimedia.org/api/rest_v1/media/math/render/svg/5a8bfe035f7a3dfaef975dfa8fbc204a3ece6456)
