Continuity correction.

Hi everyone.

I'm trying to calculate some statistics with Excel, using the
NORMSDIST function to normalize a discontinuous distribution.
NORMSDIST(z) returns the cumulative area below the distribution from
negative to positive values of z, so that NORMSDIST(z) with z<0 is
exactly the same as 1-NORMSDIST(Abs(z)).

When I calculate "z" I should apply a continuity correction, is it
right?

To do that, should I add or subtract 0.5?

z=(m-0.5-M)/s

or

z=(m+0.5-M)/s

Surfing the Net I found discordant opinions. Should I subtract 0.5
from z>0 and add 0.5 to z<0? That is, subtract 0.5 from Abs(z) and
then give back the original sign of z?

Thank you vaery much,

Antonio.

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