There are instances when your cost is based on Points (CPP) or Impressions (CPM). The quantity used to calculate this cost is the Quantity field. However, when you get to the Ratings section of the media plan, Impressions & GRPs are automatically calculated based on the data your enter. It is likely these would represent what your Quantity should be.
When you have an instance where your Quantity and respective Ratings Data is out of synch, you will receive a warning icon in the Ratings Data and be given an opportunity to synch accordingly.
In the above example, we are using a CPM rate and no quantity has been entered. However, once we entered the Ratings data, we have calculated impressions available. This is the quantity we should be running our CPM against.
The Impressions field will display a warning symbol. When clicked, you will be provided with details about the inconsistency and an option to update the Quantity field accordingly.
Once you press Update Quantity the Impressions data will be automatically populated to the Quantity field.