A range gate accepts only echoes whose depth falls inside a set interval, so echoes outside the gate are rejected. With a gate from 10 m to 14 m, depth 12 m is inside and accepted while depth 20 m is outside and rejected exactly for the stated toy gate ledger; real ultrasound depends on sound-speed estimate, timing resolution, gate and window choice, tissue variation, and measurement uncertainty.
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.