The only way to have the true grain line is to tear your fabric or pull a single thread out across the crosswise direction. Then, most often, you can tenter out the difference in the two sides as you hold it up along the fold by pulling on the fabric diagonally. Then you will know if the fabric is printed off register or not. With charms in an " I Spy" quilt it really does not make much difference. However, in applications it is very important. In those cases, if the fabric is indeed printed off register I cut my pieces to be visually perfect even if the grain is off. Most pieces are small enough or narrow enough to not be significant after the item is quilted. This used to be a very big issue in garment construction where grain line effects the hang of the garment.