The needle indicator of an electronic instrument is connected to a torsional viscous damper and a torsional spring. If the rotary inertia of the needle indicator about its pivot point is \(25 \mathrm{~kg}-\mathrm{m}^{2}\) and the spring constant of the torsional spring is \(100 \mathrm{~N}-\mathrm{m} / \mathrm{rad}\), determine the damping constant of the torsional damper if the instrument is to be critically damped.