When cooking a syrup there are different stages that are determined by dropping a small amount into a cup of cold water. For soft ball stage - after cooking syrup for awhile - drop a small amount of syrup in cold water - if you can push the mixture together into a small soft ball it's considered soft ball. Hard ball stage is when the syrup has been cooking for a longer time and when the syrup is dropped into cold water, it turns very hard - can't be shaped into a ball.

Hope this helps and enjoy the popcorn balls. These recipes are both good but if I'm short of time, the Martha Stewart recipe is quicker.