Date Parameters in Headcount Analyses

Summary:

I am just starting in OTBI Development and trying to understand how I achieve the desired analytic with results based on comparative dates.

Content (required):

I am trying to understand how I would achieve the following;

I need to present a bar chart showing the Headcount at a prompted date, alongside the headcount 1 year prior to the chosen date. (This is a simplified example to get me on the way to understanding how this is achieved).

In the Workforce Assignment - Real Time subject area there do not appear to be any date columns to filter on. I am sure the more experienced here will find this simple so forgive me if the answer is very simple.