1.) Tie a string loop around your rocket and tape it down so it does not slip. (see the picture below)

2.) Tie another string to the loop around your rocket so that your rocket is held up in the air by the string.

3.) While standing in an open place, slowly begin swinging your rocket in a circle. If the rocket points in the direction you are swinging it, the rocket is stable. If not, add more clay to the rocket nose cone or replace the rocket fins with larger ones. Repeat the stability determination instructions and then repeat the swing test.