Off the chart

when someone described a thing as "off the chart". What does he try to express?

thanks!!

My opinion is that something is "off the chart" when it is so good (or bad) that it exceeds previous measurements, etc., recorded on a chart.

UsingEnglish.com
MEANING:
If something goes off the chart, it far exceeds the normal standards, good or bad, for something.

From Urban Dictionary online:
Off the Chart
Older term... Same definition as Off the Chain.
This party is off the chart.
That girl/guy is off the chart