Two identical pendulums are connected by a light coupling spring. Each pendulum has a length of $0\mathrm{.}96$ m$,$ and they are at a place where g$=9\mathrm{.}81$ m$/$s$.$ With the coupling spring connected, one pendulum is clamped and the period of the other is found to be $1\mathrm{.}89$ s exactly. Calculate the difference in the periods between the two mode frequencies in millisecond