Retrieved from http://www.exploratorium.edu: "Once you've made all of your folds and the plane looks symmetrical, it's time to trim it, or adjust it, for flight. Give it a gentle toss forward. Your goal is to have it glide smoothly and gently to the ground, either flying straight or in a gradual curve. Make these adjustments, if necessary:
- If the nose drops and the plane dives into the ground, bend up the back of the wings. A little bend goes a long way.
- If the nose rises first and then drops, the plane is stalling. Bend down the back of the wing. Keep your adjustments small.
The comparison always involves some uncertainty. If the tape measure has marks every foot, and the table falls between the sixth and seventh marks, you can be certain that the table is longer than six feet and less than seven feet. To get a better idea of how long the table actually is , though, you will have to read between the scale division marks. This is done by estimating the measurement to the nearest one tenth of the space between scale divisions." Retrieved from Frostburg State University Department of Chemistry
You can also check this site for a tutorial on uncertainty in measurements and significant figures. http://antoine.frostburg.edu/cgi-bin/senese/tutorials/sigfig/index.cgi