I have found it more accurate and less frustrating to either use a stecil (various companies make them) or to
mark (or dot) all around the edge of the section and then connet the dots across the area. I don't have much success using the gude on the machine foot or tape as the slightest variance can cause the grid not to keep uniform.
For a square grid on the diagonal I would mark at 1" all around the square or section then connect the dots. This produces a square of about 3/4". I have found it easier and faster to then mark the grid. I have erased too many mishaped grids. You can do the same with diamonds etc. The stencil is, of course, the fastest. They are available in 12" square. Of course then can be used if block is smaller or larger.