Velocity distribution in a boundary layer is given by $\dfrac{u}{U_\infty} = \sin\large \left( \dfrac{\pi}{2}\dfrac{y}{\delta} \right)$, where $u$ is the velocity at vertical coordinate $y,\: U_\infty$ is the free stream velocity and $\delta$ is the boundary layer thickness. The values of $U_\infty$ and $\delta$ are $0.3\ m/s$ and $1.0\ m$, respectively. The velocity gradient $\left(\dfrac{\partial u}{\partial y}\right)$ (in$\ s^{-1}$, round off to two decimal places) at $y = 0$, is ________.