How do I access the number of installments for an opportunity product that is scheduled?

[nersi]

I have the question this person also had (https://success.salesforce.com/questionDetail?qid=a1X30000000dtaqEAA).

This is the scenario:

I have an opportunity with one scheduled product (scheduled for 10 equal monthly payments) and each payment is $100 which totals $1,000 for the 10 months. How can I populate a custom field at the opportunity level which takes the total amount ($1,000) and divides it by the number of installments of the scheduled opportunity product (10)? An opportunity Rollup Summary field gets me to the opportunity product but not one level lower to it's scheduled characteristics.

Any help is appreciated.