Depending on what fabric is used, sometimes a scant 1/4" must be used to maintain the block size. Thimbleberries fabrics were always printed on heavy greige back and in order to make the block come out to size a scant seam had to be used. The fabrics are now being printed on a lighter greige and I find I do not have to use that scant 1/4" anymore. If a pattern calls for scant 1/4" seams I just add the yellow inside line on the ruler, instead of cutting on the middle line. This gives me the ability to use the 1/4" seam with out adjusting anything. I also do this if I am using a good quality heavier fabric and haven't had the problem since.