In the given circuit, the voltmeter and the electric cell are ideal. The reading of the voltmeter (in volt) is __________

The electric current through ideal voltmeter is zero.
According to loop rule,

$\begin{array}{l}E-1\times i-1\times i=0\Rightarrow i=\frac{E}{2}=\frac{2}{2}=1\mathrm{A}\\ \text{ Reading of the voltmeter }=V_A-V_B=[1\times i]=[1\times 1]=1.00\mathrm{V}\end{array}$