Question 1004832
The Normal Distribution has:

    mean = median = mode
    symmetry about the center
    {{{50}}}% of values less than the mean
    and {{{50}}}% greater than the mean

<a href='http://postimg.org/image/vkq7u58rr/' target='_blank'><img src='http://s15.postimg.org/vkq7u58rr/normal_distribution_2.jpg' border='0' alt="normal distribution 2" /></a>


The number of standard deviations from the mean is also called the "Standard Score", "sigma" or "z-score".
So to convert a value to a Standard Score ("z-score"):

    first subtract the mean,
    then divide by the Standard Deviation

And doing that is called "Standardizing":

<a href='http://postimage.org/' target='_blank'><img src='http://s14.postimg.org/cx3exvtlt/standardizing.gif' border='0' alt="standardizing" /></a>