Either Jacobs ign or MSD did an exhaustive test way back & found that (at that time) that the Sears basic non dial back one was one of the few accurate ones they tested. iirc they all show retarded readings from actual timing. It was a 4 digit part # but dont remem what it was & Sears quality has deteriorated down thru the years but I love playing w my dailback but when it eventually goes bad (it's a Sears so it will) I'm gonna get an Equus one w the tach function which is very handy for serious tuning. EDIT might check eGay as there's plenty of bargains to b had