Infinitely adjustable 9 to 12 dark shade. Automatically darkens in 1/25,000 of a second . 2/4 sensors . Dark to light delay of 0.1 to 0.25 of a second . Sensitivity adjustment for low amp TIG to sunlight . Delay control for different types of welding . Automatic shutdown after 20 minutes if no arc is detected . Large viewing area . Operates on 2 AAA alkaline batteries (not supplied) . For Big Window 951 helmets and 451P and 151P helmets if manufacutred after July 9, 1994