http://www.alcula.com/calculators/statistics/correlation-coefficient/
Correlation Coefficient Calculator

The correlation coefficient, or Pearson product-moment correlation coefficient (PMCC) is a numerical value between -1 and 1 that expresses the strength of the linear relationship between two variables.When r is closer to 1 it indicates a strong positive relationship. A value of 0 indicates that there is no relationship. Values close to -1 signal a strong negative relationship between the two variables. You may use the linear regression calculator to visualize this relationship on a graph.

TI 83 TI-84 Linear Regression Tutorial Coefficient of Determination Correlation Fit Scatter Plot
https://www.youtube.com/watch?v=3uNKa_lMB5o