learning op amp comparator reference volatge

Hi...

In case of using LM3900 which is a comparator having quad op amp we need to find how many diodes and reisstors are to be connected to have a reference voltage and then compare it with incoming voltages....
to get the values of resistors and diode which will do this we need to make calculations ...iam looking forward to understand how to make those calculations....

i have its application notes and datasheet but it contains nothing related to calcutaion stuff.

Do a search for "339 circuits" or "op amp circuits." You will find plenty of detailed info.