Khan Academy : Correlation Coefficient
https://www.khanacademy.org/math/probability/scatterplots-a1/creating-interpreting-scatterplots/v/correlation-coefficient-intuition-examples
https://www.khanacademy.org/math/probability/scatterplots-a1/creating-interpreting-scatterplots/v/correlation-coefficient-intuition-examples
Wiki. seeed : project device tutorial
http://wiki.seeed.cc/Grove-Air_Quality_Sensor_v1.3/
http://wiki.seeed.cc/Grove-Air_Quality_Sensor_v1.3/
Scikit-learn : Nearest centroid and Kth nearest neighbors
http://scikit-learn.org/stable/modules/neighbors.html
http://scikit-learn.org/stable/modules/neighbors.html
Wiki pedia : Nearest centroid and Kth nearest neighbors
https://en.wikipedia.org/wiki/Nearest_centroid_classifier
https://en.wikipedia.org/wiki/K-nearest_neighbors_algorithm
https://en.wikipedia.org/wiki/Nearest_centroid_classifier
https://en.wikipedia.org/wiki/K-nearest_neighbors_algorithm