its also worth mentioning that you may be in a room where there are many different recesses to all the walls, maybe even curved walls, irregular areas so, if this is the case then you can do the following..
1. strike a chalk line parallel to the longest section of the exterior wall (exterior walls are normally? the most accurate)
2. measure the same distance from the wall at each end of the line ie 1 metre.
3. then, go to one end of the room and put you square, on the parallel line to create a 90 degree line/angle..once again, start this 90 degree line around 1 metre from the end of the parallel line you first created.
4. from these 2 lines, you can take all your measurments to each point of the room, helping you to eliminate slither cuts or at least enabling you decide on the best setting out scenario..