Percentrank Question

I have a column of values (actually the ^VIX volatility index values for the past 250 days).
If I want to know where today's value of ^VIX falls within the range over the past 250 days, I can use the PERCENTRANK function.

I recall this equation for doing a similar ranking:
(Today's value - MIN(250 days))/(MAX(250 days) - MIN(250 days))

Yet the answers from the two methods are completely different. Just what, if anything, is my remembered equation calculating?

Thanks.

I think this is what you are doing http://stats.stackexchange.com/quest...a-to-0-1-range