So basically I'm trying to figure out the distance that a person's hand is from maybe a point on the center of their chest and their bicep. I'm trying to get the position they are moving in as they attempt an exercise. I've tried using accelerometer and gyros but there error is horrible and adding a magnetic sensor and then using Kalman filtering to predict the positioning is probably out of my skill level. So I'm thinking to place magnets on the bicep, wrist and center of the chest and somehow measuring the distance between them with a magnetometer as the person is moving their arm. Is this possible? If not, are there any other options I can try.