I thought it represented the nature of the Twitter users who had had an impression of my tweets over the selected period of time. However, when I look at the absolute figures in the table expand, those figures don't match at all with the amount of followers I have.

Also, are these unique or total figures? ie: Does it calculate one unique user that has seen any of my tweets over the selected time frame, or does it accumulate that user according to the amount of my tweets he has seen during this time?

Thanks for clarifying!