Percent decrease is a measure used to indicate how much something has decreased in value or quantity compared to its previous level. It shows the proportion of reduction that has occurred and can be calculated by subtracting the new value from the original value, then dividing the result by the original value and multiplying it by 100%. For example, if a company's sales were $5 million last year but only $4.25 million this year, the percent decrease in sales would be (($5 million - $4.25 million) /$5 million) x 100% = 17.5%. This means that the company has experienced a 17.5% decline in its sales compared to last year's level.