Comparator is crafted from three redstone torches, one nether quartz, and three stone blocks arranged in the standard pattern. Unlike a repeater, this device does not boost the signal back to full strength — it instead measures and compares incoming signals, then outputs a precise analog level between zero and fifteen. This makes it the foundation of every signal-strength-aware build in the game.

The device has two modes, toggled by right-click. In compare mode (front torch off), it passes the rear-input signal through only if no side input is stronger; otherwise it outputs zero. In subtract mode (front torch on), it outputs the rear input minus the strongest side input. Most importantly, the device reads from container blocks placed behind it: a chest, hopper, brewing stand, or jukebox emits an analog signal proportional to fill level, enabling automated farms, item-counter displays, and disc players that trigger actions when a specific song plays.