BUY BY 3:00 PM CST & ITEM WILL SHIP SAME DAY M-F PLEASE MAKE SURE THIS WILL WORK FOR YOU BEFORE YOU BUY. ASK MSD MSD Performance provides award-winning technical support from M-F 8AM to 6PM MST @ MSD ONLY For Digital 6AL msd Box only # 6425 or 64253 MSD's 2-Step Rev Control allows racers to switch to a low rpm limit at the starting line. This digitally-controlled 2-Step Controller connects to the Digital 6AL's gray tach output wire and has (2) rotary dials that let you set the launch rpm in 100 rpm increments. An activation wire connects to the transbrake, a clutch switch or to the line-lock to activate the low rpm limit. When releasing the switch, the low rpm limit is turned off and the car launches hard. The rpm limit is set with the (2) rotary dials, in 100 rpm increments For Digital 6.