After many years of cutting out fiberglass cloth and ruling it with a felt-tip marker in an attempt to get a straight line when I needed one, my wife saw me doing this on the living-room carpet the other day and showed me a much better and easier way to get a straight line on the cloth. Even if you do get a nice straight rule with a nice visible line, the cloth is often skewed. What she did was just pull out one thread from the cloth. This left a nice straight, even line right across the width of the cloth. It took only a second and it accounted automatically for any skew that might be in the cloth when it is laid out on the table or on the floor. Unfortunately, it only works on the narrow dimension of the cloth. She did try to explain to me why but I'm still not sure I understand it. Suffice to say, when you want a nice straight line across the width of the cloth, pull out one thread and you will have it.