For a Radon measure μ\documentclass[12pt]{minimal}
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\begin{document}$$\mu $$\end{document} on Rd\documentclass[12pt]{minimal}
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\begin{document}$$\mathbb {R}^d$$\end{document}, define Cμn(x,t)=1tn∫B(x,t)x-ytdμ(y)\documentclass[12pt]{minimal}
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\begin{document}$$C^n_\mu (x, t)= \left( \frac{1}{t^n} \left| \int _{B(x,t)} \frac{x-y}{t} \, d\mu (y)\right| \right) $$\end{document}. This coefficient quantifies how symmetric the measure μ\documentclass[12pt]{minimal}
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\begin{document}$$\mu $$\end{document} is by comparing the center of mass at a given scale and location to the actual center of the ball. We show that if μ\documentclass[12pt]{minimal}
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\begin{document}$$\mu $$\end{document} is n-rectifiable, then ∫0∞|Cμn(x,t)|2dtt<∞μ-almosteverywhere.\documentclass[12pt]{minimal}
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\begin{document}$$\begin{aligned} \int _0^\infty |C^n_\mu (x,t)|^2 \frac{dt}{t}< \infty \mu \text{-almost } \text{ everywhere }. \end{aligned}$$\end{document}Together with a previous result of Mayboroda and Volberg, where they showed that the converse holds true, this gives a new characterisation of n-rectifiability. To prove our main result, we also show that for an n-uniformly rectifiable measure, |Cμn(x,t)|2dttdμ\documentclass[12pt]{minimal}
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\begin{document}$$|C_\mu ^n(x,t)|^2 \frac{dt}{t}d\mu $$\end{document} is a Carleson measure on spt(μ)×(0,∞)\documentclass[12pt]{minimal}
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\begin{document}$$\mathrm {spt}(\mu ) \times (0,\infty )$$\end{document}. We also show that, whenever a measure μ\documentclass[12pt]{minimal}
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\begin{document}$$\mu $$\end{document} is 1-rectifiable in the plane, then the same Dini condition as above holds for more general kernels. We also give a characterisation of uniform 1-rectifiability in the plane in terms of a Carleson measure condition. This uses a classification of Ω\documentclass[12pt]{minimal}
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\begin{document}$$\Omega $$\end{document}-symmetric measures from Villa (Rev Mat Iberoam, 2019).
