Stock averaged

The stock-averaged value accounts for the fact that appliances in current use are models that have been produced and purchased in previous years. Over these years the energy consumed by an appliance will have varied due to advances in technology.

Some appliances become more energy-efficient as technology advances, but other appliances - notably computers - now consume more energy than before.

The following example illustrates a stock average for desktop computers (without monitors) between the years 2004 and 2006.

Year	Stock in use	Energy usage kWh/year	Product
	X	Y	X*Y
2004	20738755	211.16	4379196271
2005	21657463	229.68	4974293424
2006	22505860	235.18	5292973359
	A	Sum of X*Y	14646463054
	B	Sum of X	64902078
Stock-average		A/B	225.67

So, the typical desktop computer in use in 2007 will consume 226 kWh of energy in one year.