How are POVIP and OCPIP included?

I am working on my first project with Microdata and a client asked me two technical questions about the variables:

  • How is POVIP: Income-to-poverty ratio recode calculated?
  • How is OCPIP: Selected monthly owner costs as a percentage of household income during the past 12 months calculated?

At first glance I am not seeing information on this. Can someone please point me to a resource where Census explains how these variables are calculated?