the ansatz; solid lines in Fig. \[fig:PQ2Mono\] are fits to the monopole form (\[eq:Mono\]). For monopole analysis, we utilize the form factor data in the range up to $Q^2 = 0.08~\rm GeV^2$ at $M_\pi = 296~\rm MeV$ and up to 0.10 $\rm GeV^2$ at 411 MeV, since at larger four-momentum transfers plateau signals are not clear. The fitted values of the monopole mass $M^2_{mono}$ can be used to estimate the pion electromagnetic charge radius [*via*]{} $\left<r^2\right>=6/M^2_{mono}$. Results are tabulated in Table \[table:BothDataSet\_r2\] and plotted in Fig. \[r2\_Mpi\]. The charge radius exhibits an increase as pion mass decreases.

  ---------------------------- ------------ ------------ ------------ ------------- -- --
         $\kappa_{ud}$           0.13700      0.13727      0.13754       0.13770       
   $\left<r^2\right>$(fm$^2$)   0.2174(27)   0.2538(38)   0.3129(84)   0.3352(160)     
         $\chi^2/d.o.f$          0.51(12)     1.01(12)     1.12(19)     0.44(11)       
  ---------------------------- ------------ ------------ ------------ ------------- -- --

  : Pion squared charge radius calculated from the monopole fit of data set I and II. Errors are estimated by Jackknife method with bin size of 50 $\tau$.[]{data-label="table:BothDataSet_r2"}

ChPT analysis to NLO
--------------------

For small values of momentum transfer and pseudo-scalar meson masses, we expect ChPT to provide a description of the pion form factor as a function of those variables. Here we analyze our data in terms of ChPT to NLO. The analytical 