I did some googleing as I wasnt sure of the specifics and:
# %K Periods. This is the number of time periods used in the stochastic calculation.
# %K Slowing Periods. This value controls the internal smoothing of %K. A value of 1 is considered a fast stochastic; a value of 3 is considered a slow stochastic.
# %D Periods. This is the number of time periods used when calculating a moving average of %K. The moving average is called "%D"
So it looks like by increasing the periods it is calculated over, and the smoothing, it provides less volitile readings.
