Ad tracking or campaign tracking refers to techniques used to monitor the "in-market performance" of advertising. Ad tracking uses a combination of pre-testing and post-testing. Pre-testing is used to establish benchmarks against which the actual performance of a campaign can be measured during and after the campaign has run. A particular area of concern during an advertising campaign is the problem of advertising "wear-out". When audiences are repeatedly exposed to the same message, the level of attention begins to plateau and eventually decays. Any further repetitions may cease to be noticed or may alienate target audiences. When wear-out occurs, additional advertising expenditure is simply wasted. One way that advertisers avoid wear-out is to use "repetition with variation" – that is, the use of different executions of the same message. Campaign tracking can assist advertisers to determine when to introduce a new execution of the same advertising message or to fine-tune the campaign.