Our refining and wholesale marketing gross margin is the difference between the prices of refined products sold and the costs of crude oil and other charge and blendstocks refined, including the costs to transport these inputs to our refineries, the costs of purchased products and manufacturing expenses, including depreciation.
The crack spread is a measure of the difference between market prices for refined products and crude oil, commonly used by the industry as a proxy for the refining margin.
Crack spreads can fluctuate significantly, particularly when prices of refined products do not move in the same relationship as the cost of crude oil.
As a performance benchmark and a comparison with other industry participants, we calculate Midwest (Chicago) and U. S.  Gulf Coast crack spreads that we feel most closely track our operations and slate of products.
Posted Light Louisiana Sweet (“LLS”) prices and a 6-3-2-1 ratio of products (6 barrels of crude oil producing 3 barrels of gasoline, 2 barrels of distillate and 1 barrel of residual fuel) are used for the crack spread calculation.
Our refineries can process significant amounts of sour crude oil which typically can be purchased at a discount to sweet crude oil.
The amount of this discount, the sweet/sour differential, can vary significantly causing our refining and wholesale marketing gross margin to differ from the crack spreads which are based upon sweet crude.
In general, a larger sweet/sour differential will enhance our refining and wholesale marketing gross margin.
In 2009, the sweet/sour differential narrowed, due to a variety of worldwide economic and petroleum industry related factors, primarily related to lower hydrocarbon demand.
Sour crude accounted for 50 percent, 52 percent and 54 percent of our crude oil processed in 2009, 2008 and 2007.
The following table lists calculated average crack spreads for the Midwest (Chicago) and Gulf Coast markets and the sweet/sour differential for the past three years.
## Table 0 ##
(a) Calculated using the following mix of crude types as compared to LLS.
: 15% Arab Light, 20% Kuwait, 10% Maya, 15% Western Canadian Select, 40% Mars.
In addition to the market changes indicated by the crack spreads and sweet/sour differential, our refining and wholesale marketing gross margin is impacted by factors such as: ?
the types of crude oil and other charge and blendstocks processed, ?
the selling prices realized for refined products, ?
the impact of commodity derivative instruments used to manage price risk, ?
the cost of products purchased for resale, and ?
changes in manufacturing costs, which include depreciation.
Manufacturing costs are primarily driven by the cost of energy used by our refineries and the level of maintenance costs.
Planned turnaround and major maintenance activities were completed at our Catlettsburg, Garyville, and Robinson refineries in 2009.
We performed turnaround and major maintenance activities at our Robinson, Catlettsburg, Garyville and Canton refineries in 2008 and at our Catlettsburg, Robinson and St.  Paul Park refineries in 2007.
Our retail marketing gross margin for gasoline and distillates, which is the difference between the ultimate price paid by consumers and the cost of refined products, including secondary transportation and consumer excise taxes, also impacts RM&T segment profitability.
There are numerous factors including local competition, seasonal demand fluctuations, the available wholesale supply, the level of economic activity in our marketing areas and weather conditions that impact gasoline and distillate demand throughout the year.
Refined product demand increased for several years until 2008 when it decreased due to the combination of significant increases in retail petroleum prices, a broad slowdown in general economic activity, and the impact of increased ethanol blending into gasoline.
In 2009 refined product demand continued to decline.
For our marketing area, we estimate a gasoline demand decline of about one percent and a distillate demand decline of about 12 percent from 2008 levels.
Market demand declines for gasoline and distillates generally reduce the product margin we can realize.
We also estimate gasoline and distillate demand in our marketing area decreased about three percent in 2008 compared to 2007 levels.
The gross margin on merchandise sold at retail outlets has been historically less volatile.
WOOD PRODUCTS
## Table 1 ##
FIVE-YEAR SUMMARY OF NET SALES FOR WOOD PRODUCTS
## Table 2 ##
(1) Reflects the divestitures of the company’s B. C.  coastal operations in May 2005 and North American composite panel operations in July 2006.
(2) Fiscal year 2006 includes 53 weeks of operations compared to 52 weeks in fiscal years 2002 through 2005.
FIVE-YEAR SUMMARY OF SALES VOLUME FOR WOOD PRODUCTS
## Table 3 ##
(1) Reflects the divestiture of the company’s B. C.  coastal operations in May 2005 and North American composite panel operations in July 2006.
(2) Fiscal year 2006 includes 53 weeks of operations compared to 52 weeks in fiscal years 2002 through 2005.
Net earnings Net earnings decreased primarily due to several significant, but largely offsetting, factors.
Reductions to net earnings included: ?
goodwill impairment charges of $749 million in our fine paper business in 2006; ?
a decrease of $600 million related to lower average price realizations for softwood lumber and structural panels; ?
decreased gross margins of $101 million on sales of singlefamily homes in our Real Estate and Related Assets segment; and ?
a $196 million reduction in pretax gains on dispositions.
Pretax gains of $292 million recognized during 2005 included: – $115 million on the sale of our investment in MAS Capital Management, – $63 million on the sale of the B. C.  Coastal operations, – $57 million on the sale of our French composite panel operations and – $57 million related to a deferred gain from previous timberland sales.
CELLULOSE FIBERS HOW WE DID IN 2008 We report sales volume and annual production data for our Cellulose Fibers business segment in Our Business/What We Do/Cellulose Fibers.
Here is a comparison of net sales and revenues and contribution to earnings for the last three years: Net Sales and Revenues and Contribution to Earnings for Cellulose Fibers

Tables referenced above, in order (Table 0 first):
<table><tr><td><i>(Dollars per barrel)</i></td><td>2009</td><td>2008</td><td>2007</td></tr><tr><td>Chicago LLS 6-3-2-1</td><td>$3.52</td><td>$3.27</td><td>$8.87</td></tr><tr><td>U.S. Gulf Coast LLS 6-3-2-1</td><td>$2.54</td><td>$2.45</td><td>$6.42</td></tr><tr><td>Sweet/Sour differential<sup>(a)</sup></td><td>$5.82</td><td>$11.99</td><td>$11.59</td></tr></table>
<table><tr><td>MAIN PRODUCTS</td><td>HOW THEY’RE USED</td></tr><tr><td colspan="2">RESIDENTIAL WOODPRODUCTS</td></tr><tr><td>softwood lumber</td><td>residential and commercial structures – homes, offices and stores</td></tr><tr><td>engineered lumber– solid section– I-Joists</td><td>factory-built structures, floor and roof joists, headers and beams used in residential, commercial and industrialfacilities and structures</td></tr><tr><td>structural panels– oriented strand board (OSB)– plywood– veneer</td><td>structural sheathing, sub-flooring, I-beam floor joists, recreational vehicle flooring, stepping, appearancepanels, and construction material</td></tr><tr><td>other products</td><td>complementary building products such as cedar and composite decking, siding and insulation</td></tr><tr><td colspan="2">HARDWOOD AND INDUSTRIALPRODUCTS</td></tr><tr><td>hardwood lumber and plywood</td><td>furniture, pallet cants, ties, mouldings, panels, cabinets, architectural millwork, components, and retailboards.</td></tr></table>
<table><tr><td></td><td> 2006</td><td> 2005</td><td> 2004</td><td> 2003</td><td> 2002</td></tr><tr><td>Softwood lumber</td><td>$2,997</td><td>$3,624</td><td>$3,915</td><td>$3,281</td><td>$3,186</td></tr><tr><td>Plywood</td><td>529</td><td>735</td><td>929</td><td>784</td><td>700</td></tr><tr><td>Veneer</td><td>42</td><td>44</td><td>44</td><td>39</td><td>34</td></tr><tr><td>Composite panels</td><td>357</td><td>497</td><td>501</td><td>393</td><td>379</td></tr><tr><td>Oriented strand board</td><td>939</td><td>1,164</td><td>1,390</td><td>1,109</td><td>649</td></tr><tr><td>Hardwood lumber</td><td>398</td><td>390</td><td>365</td><td>350</td><td>333</td></tr><tr><td>Engineered I-Joists</td><td>670</td><td>704</td><td>645</td><td>517</td><td>469</td></tr><tr><td>Engineered solid section</td><td>794</td><td>833</td><td>701</td><td>542</td><td>485</td></tr><tr><td>Logs</td><td>23</td><td>62</td><td>125</td><td>105</td><td>253</td></tr><tr><td>Other products</td><td>1,153</td><td>1,225</td><td>1,160</td><td>1,020</td><td>1,027</td></tr><tr><td></td><td>$7,902</td><td>$9,278</td><td>$9,775</td><td>$8,140</td><td>$7,515</td></tr></table>
<table><tr><td></td><td> 2006</td><td> 2005</td><td> 2004</td><td> 2003</td><td> 2002</td></tr><tr><td>Softwood lumber – board feet</td><td>7,871</td><td>8,650</td><td>8,890</td><td>8,981</td><td>8,623</td></tr><tr><td>Plywood – square feet (3/8”)</td><td>1,663</td><td>2,180</td><td>2,629</td><td>2,665</td><td>2,685</td></tr><tr><td>Veneer – square feet (3/8”)</td><td>215</td><td>231</td><td>225</td><td>239</td><td>218</td></tr><tr><td>Composite panels – square feet (3/4”)</td><td>802</td><td>1,229</td><td>1,234</td><td>1,162</td><td>1,092</td></tr><tr><td>Oriented strand board – square feet (3/8”)</td><td>4,096</td><td>3,948</td><td>4,213</td><td>4,361</td><td>4,205</td></tr><tr><td>Hardwood lumber – board feet</td><td>412</td><td>427</td><td>417</td><td>435</td><td>435</td></tr><tr><td>Engineered I-Joists – lineal feet</td><td>456</td><td>484</td><td>496</td><td>447</td><td>400</td></tr><tr><td>Engineered solid section – cubic feet</td><td>36</td><td>38</td><td>37</td><td>32</td><td>28</td></tr><tr><td>Logs – cunits (in thousands)</td><td>169</td><td>451</td><td>934</td><td>799</td><td>1,657</td></tr></table>

Question: by what percentage did the average crack spread for the midwest ( chicago ) decrease from 2007 to 2009?
Answer: -0.60316
Reasoning program: subtract(3.52,8.87), divide(#0,8.87)