First we measure the distance from each observer to the launch site. A distance of 100 - 150 metres is recommended.
Students work in pairs. One looks through the inclinometer at the rocket and stops at the rocket's highest point. The other team member reads the angle which the string has stopped at.

According to the inclinometer on the left the angle is 20 degrees.

Record each groups angle on a table.

Now its time to calculate the height.