You will need the following materials: a rigid transparent plastic tube approx. 14mm in diameter and 31cm in length, with plastic or rubber stoppers on each end, a spring (1.5g/cm), about three cm unstretched; a mass (approx 10g), paper clip,7"x 1/8" rubber band, correction tape 1/6" wide, 1" wide tape.
Attach the sinker to the spring and apply a small bit of tape so that it will not detach.
Carefully bore a small hole (the diameter of the paper clip) through the stopper and plastic tube.
Remove the stopper with the hole from the plastic tube. Place the free end loop of the spring into the stopper so that when the paper clip is put through the holes, the loop will become hooked. While holding this part of the assembly upside down, place it into the tube. Align the holes in the tube with those in the stopper. Unbend a paper clip and insert it through the holes in the tube and stopper out the other side. this takes some patience.
Invert the assembly to verify that the spring has been looped. Bend the rest of the paper clip (trim if necessary) and tape the ends to the tube. This keeps the sharp ends from catching or damaging anything. Glue the remaining stopper to the other end of the tube.
Hold the spring accelerometer horizontally. around the clear tube, mark the bottom point of the spring's extension with the 1/6" tape--this is 0. Now, hold the spring accelerometer vertically and do the same--this is one. These are calibration points. Assuming the spring stretches in a linear (a constant amount for each increase in weight/g-force) fashion, subsequent uniform spacing can now be marked (the distance between 0 and 1 is the same as the distance between 1 and 2, 2 and 3, 3 and 4). Secure the rubber band to the bottom of the tube as a tether. Please use the rubber band or some other method of securing the accelerometer to you so that you do not accidentally hit another passenger with the tool. If you notice at most amusement parks, there are coins, etc, on the ground beneath many coasters and rides, things most passengers never intended to lose.
Holding the accelerometer upright will tell you the amount of g-force pulling you down, or in a loop, holding you in your seat. If you hold the accelerometer vertically, pointing the spring toward your direction of movement and the weight toward your body, you can measure how much force is being exerted as you move forward. On a ride like Spin Out, or the Typhoon, where you are pressed against a wall on a spinning chamber, point the spring toward the center of the circle, and the accelerometer measures how much force is being exerted by the wall to push you inward (making your movement circular rather than straight).