  The backreaction of inhomogeneities describes the effect of inhomogeneous
structure on average properties of the Universe. We investigate this approach
by testing the consistency of cosmological $N$-body simulations as non-linear
structure evolves. Using the Delaunay Tessellation Field Estimator (DTFE), we
calculate the kinematical backreaction $Q$ from simulations on different scales
in order to measure how much $N$-body simulations should be corrected for this
effect. This is the first step towards creating fully relativistic and
inhomogeneous $N$-body simulations. In this paper we compare the interpolation
techniques available in DTFE and illustrate the statistical dependence of $Q$
as a function of length scale.
