Two Signal Devices on Fern Pass Trail

Messages Across a Trail Bend

A fourth-grade class is planning a cleanup on Fern Pass, a mountain trail. Two groups will stand at wide resting areas where they can see each other across a bend. They want to send four short messages without shouting. Before the cleanup, the class compares two signal devices. These are practice messages, not emergency signals.

The first device is a pattern board. It shows three large squares in a row. Each square is black or white. The receiver reads the squares from left to right. The sender turns the board toward the receiver, holds it still, and lowers it. One complete board signal takes 7 seconds.

The second device is a signal lamp. A button plays three flashes in order. Each flash is short or long, with a small dark gap between flashes. The receiver watches from the first flash to the last. A complete lamp signal, including a dark pause at the end, takes 4 seconds.

Both groups carry the same code key. In the key, each white square matches a short flash, and each black square matches a long flash. A square or flash alone is not a whole message. The receiver must notice the complete pattern and its order.

For the comparison, the class uses the same two resting areas and the same readers. Each device sends the same list of ten messages in bright sun and then in shade. Some messages appear more than once. The class records how many whole messages are read correctly. Students stay in their resting areas during every trial.