There are two reasons to check wall deflection: to assess the scope of plastering, and to inspect the quality of the work performed.
Even visually straight walls can pretty much deviate from the reference plane. Therefore, estimation by sight is not a reliable technique. There are several ways to find dimples and humps on a wall surface.
Using a 2-metre builder’s level would be sufficient for most residential premises.
Chose a level by a reputable brand in order to avoid instrumental errors.
Apply the level to the wall every 1.5-2 metres in vertical and horizontal planes. Make sure there are no gaps or extensions between the level and the wall surface. A brand-new trapezoid rule can be used as a level, though.
Light beam test
The quality of wall coating can be tested with a flashlight or any other compact light source. Just direct the light beam parallel to the wall, and every imperfection will be seen as a shadow. It is better to perform the light beam test in darkness, lest the scattered light from the windows would visually mask the defects.
Plumb bob test
You can make a plumb bob or a pendulum yourself, with a string and a small weight. Then check, whether the surface is level against the string line, applying the string end to the wall.
Laser level test
Run a laser level, or linear laser levelling device, in the vertical plane contouring mode and place it as close to the wall as possible. The device shall project an absolutely straight laser beam onto the inspected surface, and a laser plane shall appear between the wall and the instrument. Apply a ruler with a millimetre scale perpendicular to the wall, and the laser beam shall cross the ruler plane, indicating the size of the gap between the vertical laser plane and the wall. Further, apply the ruler to other points of the wall and compare the readings. The closer the results, the more even the surface.
Furniture and shelves are rectangular. That is why it is important that the room corners are precisely 90 degrees in order to allocate the furniture accurately and promptly.
Using a tape measure is the easiest way to check angles: just make sure that the diagonals are equal, as well as the opposite walls.
Also, a builder’s square with at least 50-cm arms can be used to check angles. Check the whole height of every corner, applying the square with small increments.
Further, check the geometry and the depth of the door openings and window openings. It can be done with a builder’s level. Pay particular attention to the challenging zones like power outlets, pipes, network inlets and outlets, platband and baseboard junctions.