Draw an angle of $80^o$ with the help of a protractor and bisect it. Measure each part of the bisected angle.

Steps of construction:

Construct a ray $OB$

Using the protractor construct $\angle AOB$ of $80^o$

Considering $O$ as centre and convenient radius construct an arc cutting the sides $OA$ and $OB$ at the points $Q$ and $P$

Considering $Q$ as centre and radius more than half of the angle $PQ$, construct an arc

Considering $P$ as the centre and radius more than half of the angle $PQ$, construct another arc which intersects the previous arc at the point $R$

Join the points $OR$ and produce it in order to from a ray $OX$

Therefore, $OX$ is the bisects of the $\angle AOB$

So the measure of each parts of the bisected angle is $\angle AOX=\angle BOX=40^o$