that for smeared source. Since the computing time is still $4/12=1/3$ for the random wall source, we employ the method of random wall source with 4 sets of random wall sources in our measurements. In addition we repeat measurements with the source located at $t=0,16,32,48$ since the time extent of our lattice is 64.

Measurements
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We apply our calculational setup to a subset of the PACS-CS gauge configurations [@pacscs] corresponding to the degenerate up-down hopping parameter in the set $\kappa_{ud} = \{0.13700$, $0.13727$, $0.13754$, $0.13770\}$. The hopping parameter of strange quark is fixed at $\kappa_s = 0.1364$.

The first set of measurements, which we call data set I, is made with an exponentially smeared source and local sink, setting the final pion at zero momentum $\vec{p'}=\vec{0}$ and varying that of the initial pion $\vec{p}$ in the three-point function. The fixed sink time $t_f$ in the ratio (\[eq:ratio\]) needs to be chosen large enough to eliminate excited states contributions. However, statistical fluctuations increase as $t_f$ increases, and examining measurement results, we choose $t_f=24$ to balance the two opposite features. The twist technique is applied to the quark running from the source to the current. Two values are chosen for the 