Why is it necessary to equalize water levels in the buret and the leveling funnel?

So that the pressure will be at constant. If the water level will have raised up in the graduated tube directly above the water level in the burets and levelling funnels, the pressure on the trapped gas is no longer at usual atmospheric pressure. It produces a tapping effect on the locked in gas therefore dropping the pressure. If the burets and levelling funnels will be dropped below water level the reverse effect is produced.

It is necessary to equalize water levels in the buret and the leveling funnel so that there will be a constant pressure are. If the water level raised up in the graduated tube directly on top of the water level in the burets and leveling funnels, the pressure on the treed gas is not any longer at usual air pressure. It produces a sound impact on the bolted gas that causes the pressure to drop. If the burets and leveling funnels are below the water level the reverse impact will happen.