Scratch Boards are a way of connecting real world sensors to your projects. 
The Scratch board has a sound sensor, a light sensor, a push button, a slider and alligator clips that can measure the electrical resistance in a circuit.  It converts to the computer via a supplied serial to USB cable.

You can find out more about the Scratch board or purchase one from the official Scratch site. 

In the Sensing block library, you will find two special blocks for use with the Scratchboard.  They are

The first block can show values for the slider, light, sound and the 4 resistance sensors.

The second block senses whether the button is pressed, or the A,B, C or D resistance sensors are touching.

If you right click on either of these blocks you get an option to show the Scratchboard watcher.  This will add a watcher to the stage area showing the value of all the sensors at any time.

This script will change the height of the cat depending on where you push the slider.