[${}^{1}\mathrm{S}_{0}$]{} wave at $k\approx370\;{\ensuremath{\mathrm{MeV}}}$ and [${}^{3}\mathrm{S}_{1}$]{} wave at $k\approx90\;{\ensuremath{\mathrm{MeV}}}$ and $400\;{\ensuremath{\mathrm{MeV}}}$ [@Epelbaum:2014efa]. As the qualitative plot in Fig. \[fig:qualitative\] shows, the corresponding spikes may make it more difficult to determine slopes.

[**Fitting to a Point**]{} A “zero” in eq.  is induced intentionally when the observable contains a LEC that is determined in the channel in which one tests the PC. If the observable is tuned to exactly reproduce a certain value at some point $(k_0,{p_\text{typ}})$, then ${\mathcal{O}}(k_0;\Lambda_1)-{\mathcal{O}}(k_0;\Lambda_2)=0$ – with all the problems mentioned just now. Obviously, one should choose the fit point to be outside the slope-region. In the example of Sect. \[sec:application\], the strength of the $3N$ interaction $H_0$ without derivatives was fixed at each order to the $Nd$ scattering length, i.e. using $k=0$ as fit point. That is far away from the slope-region. At [N${}^{2}$LO]{}, the momentum-dependent $3N$ interaction $H_2$ was in addition determined from the triton binding energy $B_3=8.48\;{\ensuremath{\mathrm{MeV}}}$, i.e. the pole in the amplitude is fixed to $k_0=\sqrt{-4M
  B_3/3}\approx100\;{\mathrm{i}}\;{\ensuremath{\mathrm{MeV}}}$. If one chooses this fit point for $H_0$ at LO and NLO, instead of $k_0=0$, the pattern of the slopes is wiped out; see Fig. \[fig:toB3\]. It appears that fitting only at $k_0$ introduces a new low-energy 