All 144s from the 1950s were made with a viewing window; a model without a window did not exist. The celluloid of the window can, however, darken strongly over the course of decades and appear dark red to almost black. Dried ink residues inside can also visually close the window. Multi-day flushing with water often brings the window better into view again; with moderate water hardness, tap water suffices; otherwise distilled water is recommended.