Included in the Sandbox AR app is a Measuring Tool which students can use to find out how big the models are.

To open the Measuring Tool, click on the ruler icon in the left-hand menu.

Select New Measure and then place your first 'node' (marker).

Place a second 'node' and the app will tell you the distance between the two nodes.

You can change the units of measurement using the toggle in the top right side of the screen.

The Measuring Tool can be used in both table scale and life scale.

Select Stop Measure to stop using this function. 
The measurement will remain visible but if you would like to hide this, open the Measure tool again and tap Toggle Visibility in the bottom right-hand corner.