In the model, b is the length of a rigid segment, N is the number of segments of length b , R is the distance between the fixed and free ends, and L c is the "contour length" or N b . Above the glass transition temperature, the polymer chain oscillates and r changes over time. The probability distribution of the chain is the product of the probability distributions of the individual components, given by the following Gaussian distribution: P ( R → → ) = P ( R x ) P ( R y ) P ( R z ) = ( 2 n b 2 π π 3 ) − − 3 / 2 exp ⁡ ⁡ ( − − 3 R 2 2 N b 2 )