Have 2 great demonstrations in 1 unit. Demonstrate the principle of acoustical resonance and audible beats with this set of high-quality resonators. When you place the openings close to each other and strike only 1 tuning fork, the other fork will vibrate sympathetically (C-256 Hz). To demonstrate beats, slide the weight of the adjustable tuning fork to change the frequency. Includes a rubber mallet and instructions. Minor assembly required.