Active strain gauges are connected in a half-bridge configuration to measure strain in a cantilever element. When powered by a voltage source of $10$ $\mathrm{V}$, the voltage at the output of the bridge is $1$ $\mathrm{mV}$. If the gauge factor is $2.5$, the strain in the cantilever element is $\_\_\_\_$ microstrain.
- $40$
- $80$
- $20$
- $160$
