The device for measuring the current or emf is connected within the circuit of the thermocouple. It measures the amount of emf flowing through the circuit due to the two junctions of the two dissimilar metals maintained at different temperatures. In figure 2 the two junctions of the thermocouple and the device used for measurement of emf (potentiometer) are shown.
I think that this is what advertisers are shooting for when they pay the big price to get their ads up there. Regular billboards are just as effective as ever, even though there are now digital billboards being made that can have multiple ads on them and switch between them every few seconds.
Pop-up and pop-under ads annoy many users because they clutter up the desktop and take time to close. However, they are much more effective than banner ads. Whereas a banner ad might get two to five clicks per 1,000 impressions, a pop-up ad might average 30 clicks. Therefore, advertisers are willing to pay more for pop-up and pop-under ads. Typically, a pop-up ad will pay the Web site four to 10 times more than a banner ad. That is why you see so many pop-up ads on the Web today.