If a tracing inquiry for an individual arrived at the ITS, or if one is now sent to the Arolsen Archives, a T/D (tracing/documentation) file is created. The Arolsen Archives have a total of around 2.3 million of these correspondence files, and roughly another 10,000 are added every year. These files are assigned a number known as the T/D number. All T/D files and correspondence files that are more than 25 years old are currently being digitized and can be accessed for research purposes in the Arolsen Archives.