Abstract: Wireline operation depth control in cased wells can be substantially improved by attaching a combined magnetic and radioactive marker to the casing in the vicinity of the zone of interest. A cased hole log is then performed, such as a perforation depth control (PDC) log, using both a casing collar locator and a gamma ray sensor. The marker produces distinctive spikes on the logs from both sensors. The casing collar log is tied in to the gamma ray log simply by aligning these distinctive spikes on both logs. This helps to ensure that subsequent cased hole wireline operations, such as perforating, that rely solely on a collar locator for depth control are performed at the correct depth.