Hydrostatic Paradox - weighing issue In the picture below, both tubes have the same pressure at the bottom. I understand that if they were weighed individually, they would show a different result since the water on the second tube is exerting an upward force on the "roof", removing "excess" force on the scale.
But what if the scale was put inside the tubes (red lines)? Also, the sides of the tubes are mounted onto an immovable wall, preventing any upward force affecting the scale from below. Now since pressure = Force/area, and area and pressure are the same in both, the scales must be subjected to the same forces as well. Will the second scale now show an incorrect result?

 A: Indeed, assuming your scales still work and have negligible volume (to avoid issues with buoyant forces), they'll now show the same reading. I wouldn't say that means the scale is "wrong". It's designed to measure the normal force exerted on its top part, and in both cases it's doing just that.
A: I assume that by incorrect you mean the same "weight". Yes it will show the same weight, and the reason it will not show the actual weight is that the slanted part of the wall is making a force, the reaction to the water pressure force larger than if the wall were straight (because of the larger pressure with depth), into the liquid. On the otherhand your first paragraph has a mistake, if you put the balance outside the weight will be different not because of the upward force. This force is irrelevant because the water is not in contact with the scale and then that has to be considered an internal, not an external, force. In such a case the weight will be different because they have different mass in absence of external forces. 
