Not everyone has to be a six sigma black belt to appreciate and use a well-designed control chart. The top and bottom red lines indicate a standard deviation away, the green line indicates the average, and the black line indicates the values over time. Here's an easy parameterized snippet to generate the chart type:

Title: control_chart(table,value_field,x_axis)

select
  [x_axis]
  , [value_field]
  , average
  , average - stdev as stdev_minus_one
  , average + stdev as stdev_plus_one
from
  [table]
  , (
    select
      avg([value_field]) as average
    from
      [table]
  )
  as a
  , (
    select
      stddev_samp([value_field]) as stdev
    from
      [table]
  )
  as s