Cal. 938 appeared around 2000 and eventually replaced the similar Cal. 928, carrying the standard for one of Jaeger-LeCoultre's signature complications, the "Réserve de Marche, or power reserve indicator. The company was the first to bring this complication to market in 1948 with the Cal. 481 Powerwind and has continued to market watches with this complication to today.
Cal. 938 an automatic movement made up of 273 components. It runs at 28,800 A/h, has 41 jewels, and a power reserve of 43 hours. It features central hour and minute hands and small seconds at 6:00. A subdial at about 2:30 shows the date by pointer.
But it is the retrograde power reserve pointer centered at 10:30 that gives the movement its claim to fame. It swings counter-clockwise from about 6:30 to about 4:00 and features a scale marked "0 - 10 - 20 - 30 - 40" and the "Réserve de Marche" title.
Jaeger-LeCoultre currently uses this calibre in a single watch model, the Jaeger-LeCoultre Master Ultra Thin Réserve de Marche. Cal. 938/1 is substantially similar.