Working out time periods for OIscillators

[Ben Clayton <s319017@xxxxxxxxxxxxxxxxx>]

Giday from Australia

This is my first entry and the question is a pretty dumb one.  
How do you work out how many days you put in for the formulas for the
RSI and the Stochastic Oscillator.

I am using 13 for both and this seems to work.  I wondering if some one
out there can tell me how they work out what numbers to use.


Also with open interest, how do you get graphs of these.  This is in
relation to options.

Thanks in advance.
Ben