Excel works with 16 digits and rounds to 15 digits for display.

Once NORMSDIST(x) (or anything) gets above 15 and a half nines, it's 1. It
happens at about NORMSDIST(7.87375095140855).

Tim C


"crapatmath" wrote in message
...
Hi All,

Why is
1-NORMSDIST(7.8) = 3.10862e-15
while
1-NORMSDIST(7.9) = 0

Is there a limit to how far out the Gaussian PDF curve you can go before
Excel rounds to zero?

Thanks

Barry