Guys, a 3mph error over the whole range is a "bias error" and is not caused by a ratio adapter. The ratio adapters correct the slope of the VSS period so you would have a linear error, IE 1mph at 10mph, 2mph at 20mph, 3mph at 30mph, etc... I know for a fact that there are indeed bias errors in the speedos also. In fact, either Car&Driver or Motortrend one ran an article on it recently... If you really want, you can pick a mph that you want it to be exact, email me with indicated mph actual mph and current switch settings and I can fudge it for that point. Please note however that it will introduce a slope error over the rest of the speed range. And again, this is not a ratio adapter issue, it is a speedometer metering issue.