anchor.diff:  (default value used in the previous example), the function uses the last key
   of the window as the key of the aggregated value. When you specify 
   `Boundary.AtEnding`, the last key is used, so the values can be nicely 
  -aligned wiht original values. When you want to specify custom key selector,
  +aligned with original values. When you want to specify custom key selector,
   you can use a more general function `Series.aggregate`. 
   
   In the previous sample, the code that performs aggregation is no longer
  
positive.code:   [ stock1 (TimeSpan(0, 1, 0)) 1000 |> Chart.FastLine
      stock2 (TimeSpan(0, 1, 0)) 1000 |> Chart.FastLine ]
  (**
  The above snippet generates 1k of prices in one minutte intervals and plots them using the
  [F# Charting library](https://github.com/fsharp/FSharp.Charting). When you run the code
  and tweak the chart look, you should see something like this:
  
  
negative.code: // Sum each column and divide results by a constant
  Frame.sum df / 6.0
  // Divide sum by mean of each frame column
  Frame.sum df / Frame.mean df
  