different manufacturers have different ways of 'reading' the numbers, for example, for Easton arrows, the lower the number the 'stiffer' the arrow, or less flex, where as for something like Carbon Express the higher the number the stiffer the arrow, you have to do some research as the right arrow is the difference between hitting the bullseye or not, basically saying, the higher poundage bow, the 'stiffer' the arrow should be to avoid damage to your bow or even you.