Deflation

deflation
a slowing of the economy characterised by falling prices and wages, the reverse of inflation
delayed quotation pricing ...

That is, two years later, the computer has not only declined in price by 20%, but it may also be 30% better (based on an index of speed and other performance factors). In that case, then, there has actually been, over the period, a net deflation of ...

See also: Cycle, Services, Objective, New Products, Needs