https://owl.english.purdue.edu/owl/resource/590/1/ 

http://cfaresources.s3.amazonaws.com/AA%20General%20Studies/AA%20Revisions%202016/Leverage%20Business%20Tools/BytheNumbers-CellReferencesFormulasandFunctionsinGoogleSpreadsheets.pdf

https://www.youtube.com/watch?v=_-fRzqnu3BA

https://www.youtube.com/watch?v=A6MmdLR3VK0