Question

What does plots must be accurate to half a small square mean when drawing a graph?

Answer 1

If you have a piece of graph paper, it will be divided into squares.

If you must plot 2.5 on the graphing paper, you need to accurately show that 2.5 as

If you must plot 2.25, you need not be as accurate, but you should be between 2 and 2.5. The same applies for anything smaller than or bigger than 2.5. So 2.7, needs to be seen as being between 2.5 and 3.0, but not necessary at exactly 2.7.