A dc voltage with ripple is given by $v(t)=\left [ 100+10\sin\left ( \omega t \right )-5\sin\left ( 3\omega t \right ) \right ]$ volts. Measurements of this voltage $v(t)$ made by moving-coil and moving-iron voltmeters, show readings of $V_{1}$ and $V_{2}$ respectively. The value of $V_{2} − V_{1}$, in volts, is ________.