I'm trying to duplicate the chart found at
http://www.aheadofthecurve-thebook.com/07-03.html. How do I calculate
real personal consumption expenditures trailing three months?

It is a simple calculation.  For any point in time, take the previous
three months of real personal consumption expenditures and add them
together.  That gives you real personal consumption expenditures
trailing three months.

The graph shows % change vs. prior year.  I will calculate the value
for the beginning of 2005 to show you how to replicate the chart.  In
this case, you would take the value for 2004 (IV) (the trailing three
months), subtract the value for 2003 (IV) (the trailing three months
for the prior year), and then divide that amount by 2003 (IV) to get
the % change vs. prior year.

These figures are available at:  "Table 2.3.3. Real Personal
Consumption Expenditures by Major Type of Product, Quantity Indexes"
US Department of Commerce
http://www.bea.gov/bea/dn/nipaweb/TableView.asp?SelectedTable=63&FirstYear=2003&LastYear=2005&Freq=Qtr.

2004 (IV) is 114.236.  2003 (IV) is 110.046. 
(114.236-110.046)/110.046 = 3.8%.  This value matches the value of the
black line on the chart you provided at the beginning of 2005.

Sincerely,

Wonko

Search terms:   "real personal consumption expenditures"

Thank you. It was a simple question, but, amazingly, nobody I work
with could answer it.