spatial resolution were employed in their analysis. Their values of drag reduction at $Re_\tau=200$ are lower than ours and their drag reduction variations with $Re_\tau$ at $W_m^+=10$ are more significant, namely 11.2% at $T^+=50$, 25.1% at $T^+=100$, 29.9% at $T^+=150$, and 29.3% at $T^+=200$.

Previous experimental studies indicate that the drag reduction does not vary with the Reynolds number for (low) values of this parameter. For example, @ricco-wu-2004 have found that in a turbulent boundary layer the drag reduction does not change as the Reynolds number based on the momentum thickness $\theta$ and the free-stream velocity $U_\infty$ increases from $Re_\theta$=500 to 1400 (which correspond[^2] to $Re_\tau$=257 and $Re_\tau$=633), when $D_m^+ \approx 240$. @choi-graham-1998 have shown that in a pipe flow modified by circular wall oscillations the wall-shear stress reduction remains within the range of the experimental uncertainty when the Reynolds number $Re$ based on the bulk velocity and the pipe diameter increases from $Re$=23,300 to 36,300 (which correspond[^3] to $Re_\tau=650$ and $Re_\tau=962$). The uncertainty range on the [*percent*]{} drag reduction was about 10% for @ricco-wu-2004 (see Table 1 at page 45 in their paper), and about 20% for @choi-graham-1998 (see Fig. 2 at page 8 in their paper). It was 