  One major systematic uncertainty of lattice QCD results is due to the
continuum extrapolation. For an asymptotically free theory like QCD one finds
corrections of the form
$a^{n_\mathrm{min}}[2b_0\bar{g}^2(1/a)]^{\hat{\Gamma}_i}$ with lattice spacing
$a$, where $\bar{g}(1/a)$ is the running coupling at renormalisation scale
$\mu=1/a$ and $n_\mathrm{min}$ is a positive integer. $\hat{\Gamma}_i$ can take
any positive or negative value, but is computable by next-to-leading order
perturbation theory. It will impact convergence towards the continuum limit.
Balog, Niedermayer and Weisz first pointed out how problematic such corrections
can be in their seminal work for the O(3) model. Based on Symanzik Effective
Theory for lattice QCD with Ginsparg-Wilson and Wilson quarks, various powers
$\hat{\Gamma}_i$ are found due to lattice artifacts from the discretised
lattice action. Those powers are sufficient when describing spectral
quantities, while non-spectral quantities will require additional powers
originating from corrections to each of the discretised local fields involved.
This new input should be incorporated into ans\"atze used for the continuum
extrapolation.
