An ideal selection window accepts ratios inside its exact bounds. 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 pass window has inclusive bounds
The ideal pass window runs from ratio 3 through ratio 5.
3≤m/z≤5
Inside passes and outside rejects
Ratio 4 passes, while ratio 6 rejects. This is not a quadrupole field simulation.