Refresher on NPV

https://hbr.org/2014/11/a-refresher-on-net-present-value/

I ran across this HBR.org article on net present value (NPV).   Although all of the material was covered in our class,   I thought it was a good refresher for our NPV discussions in class and our assignments.   The author covered several points below.  I found the last point to be the most interesting and helpful.      

1. What is NPV?  -  it is a method of calculating return on investments for a project or majotr expenditure. 
2. What are NPV used for?  -   It is the "tool of choice"  for most financial analyst because is considers time value of money and provides a concrete numbers that can be used for comparison purposes.   
3. How do you calculate?  -  the author points to excel as the main tool along calculator, with NPV function, and phone apps.  He goes on to explain the formulas and math behind the calcs.
4. What are some Common Mistakes?   - 
1. It is hard concept for other non-financial  people to understand
2. Calculations are based on assumption and estimates,  which means there is lots of room for errors.   
3. Risk associated with future discount rates.,  interest rate could spike in the future.    
4. Mistakes are often made with project future returns.  You need to be certain about returns,  all too often they are over optimistic.