A range gate accepts and rejects by checked depth. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
The depth inside the gate is accepted
The gate runs from 10 to 14 meters, and depth 12 meters lies inside.
10≤12≤14
The depth outside the gate is rejected
The later echo has depth 20 meters, which is outside the same gate.