CTA is an abbreviation for Central Train Pointer. Electronically / mechanically functioning indicators on the platforms, which indicate what time and where the next train leaves from the platform in question. The CTA's were introduced in the 1970s, mostly still in test versions and at different stations just slightly different from each other. In the 1980s, the most commonly used model went into circulation. Standardization also became a fact. The blue areas with track number were always closest to the track in question. The white areas with text indications and the clock therefore always hung more to the centerline of the platform. The pole was also always positioned towards the centerline or back of the platform, with which the arm pointed to the relevant track. These CTA's, with folding roll system, were replaced around 2010 for TFT screens.
Tip for the detailers among us: The track number and the final destination can be entered per set of CTAs. If desired, the track number can be supplemented with an A or B, which occurs on longer platforms. E.g. 1a or 24b.