Percent Change = New Value − Old Value|Old Value| × 100%
Example: There were 200 customers yesterday, and 240 today:
240 − 200|200|× 100% = 40200 × 100% = 20%
A 20% increase.
Percent Error = |Approximate Value − Exact Value||Exact Value| × 100%
Example: I thought 70 people would turn up to the concert, but in fact 80 did!
|70 − 80||80| × 100% = 1080 × 100% = 12.5%
I was in error by 12.5%
(Without using the absolute value, the error is −12.5%, meaning I under-estimated the value)
The difference between the two is that one states factual calculations and the other is a theoretical guess