Redstone Comparator
A redstone comparator measures and compares analog signal strengths. In comparison mode it passes the back signal unless a side is stronger; in subtraction mode it outputs the back minus the strongest side.
What does a comparator do?
A redstone comparator works with the strength of a signal, not just on/off. It has one output (front) and three inputs: a main signal at the back and two side inputs. The single front torch tells you the mode — unlit is comparison mode, lit is subtraction mode — and you tap the comparator to switch between them.
Its superpower is reading things: point a comparator at a chest, furnace, or other container and it outputs a signal proportional to how full that container is.
Comparison vs. subtraction mode
In comparison mode (front torch off) the comparator passes the back signal straight through — unless one of the side inputs is stronger, in which case the output drops to 0. It answers the question “is the back at least as strong as the sides?”
In subtraction mode (front torch lit) it outputs the back signal minus the strongest side signal. Back 15 with a side of 6 gives an output of 9.
Reading signal strength visually
Because the comparator preserves analog levels, you can fan a signal out across a row of lamps or dust to make a bar graph — a quick way to see how strong a signal is. This is the basis of container monitors, item sorters, and fill indicators.
Key facts
- Two modes: comparison (torch off) and subtraction (torch lit); tap to toggle.
- Reads container fullness — output strength scales with how full a chest, furnace, or hopper is.
- Side inputs only ever reduce or gate the output; the back is the main signal.
- Has a fixed delay of 1 redstone tick (0.1s).
- Does not boost weak signals back to 15 the way a repeater does — it preserves the analog level.
Bedrock note
Comparator math and container-reading behave the same in Bedrock as Java for the everyday cases shown here. Where the two editions can diverge is in exotic update-order and 0-tick setups; for reliable builds, keep comparator chains simple and add a repeater if you need the signal refreshed to full strength afterwards.