A student in the laboratory measures thickness of a wire using screw gauge. The readings are $1.22 \mathrm{mm},1.23 \mathrm{mm},1.19 \mathrm{mm}$ and $1.20 \mathrm{mm}$. The percentage error is $\frac{x}{121}\%$. The value of $x$ is _____ .

The average value of the readings is $x_{\mathrm{avg}}=\frac{1.19+1.20+1.22+1.23}{4}=1.21$

Now, absolute error in measurement $\Delta x_{\mathrm{avg}}=\frac{0.02+0.01+0.01+0.02}{4}=\frac{0.06}{4}=0.015$

Percentage error in measurement is $=\frac{0.015}{1.21}\times 100\%$$=\frac{150}{121}\%$

So, the value of $x=150$.