A play is a showing; an impression is a likely viewing. How JOLT counts plays from the screen, turns them into impressions with audience measurement, and bills on the result.
Every time your 8-second spot is shown, the screen's player records a play with the screen, the creative and the time. Those records are collected from the network several times a day and are the base of both your report and your invoice. A play that was scheduled but not shown — because a screen was offline, say — is not counted and not charged.
A play on a busy supermarket entrance is seen by more people than a play in a quiet car park. Each JOLT screen carries an impressions-per-play measure from independent audience measurement of the traffic past that screen, by time of day and day of week. Impressions = plays × that measure.
The figure varies by screen and by market. In the report you can see impressions per play by screen, which is why two screens with the same plays show different impressions.
Before a campaign runs, and for screens with no measured history yet, the forecast uses the market's average impressions per play. The report labels which basis it used — measured playout, network average or modeled estimate — so you always know how firm a number is. Billing is always on actual plays.
The age and household mix shown in the report comes from census data about the neighborhoods around the screens. It describes residents, not the people counted passing the screen, and JOLT labels it that way. See Audience filters.