How are percent error and percent change similar

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