The device has Acc 2.4 control unit, decoder (encoder) and machine console, suitable for steel folding machines. The three-part window fold (altar fold) is a type of fold popular with graphic designers, but with the previously available folding technique, it demanded a great deal of experience and tact on the part of the bookbinder in order to complete the job in the calculated time with good fold quality. The pneumatic gatefold pocket is controlled digitally, and the deflection profile is opened and closed pneumatically. The ACC 2.4 digital control unit precisely regulates the switching times — individually and independently of the folding speed. Precise control of the deflection profile enables minimum flap gaps of just 0.5 to 1.0 millimeters, depending on the paper thickness. Even in continuous operation, high cycle rates (up to 15,000 cycles/hour) are possible without any problems.