Baselines let you display your current project dates and compare them to the original plan. To turn baselines on, go to Home > Project View Properties > Task Bars and check the Baseline Markers. OnePager will import your baseline information and display it below the main task bar:
If you have milestones in your chart, you can go to the Milestones tab and enable baselines there as well, if you like.
To change the format of your baselines, go to Home > Project View Properties > Task Bars (or Milestones) and click on the Baseline Properties button. This enables you to pick a different color, shape, or style of your baseline markers.
Using a Different Baseline
By default, OnePager uses the standard Microsoft Project baseline. However, any pair of date fields can be used in its place. To change which fields are displayed as a baseline, go to Home > Project View Properties > Field Mappings: