Yes im aware of those devices as well. We sell them at repco and i might consider one if my other options to recalibrate the speedo / speed sensor dont pan out. However there is another option which ive discovered and its a little control device which you plug into your speed sensor loom and it modifies the pulse signal from the sensor to the ecu to calibrate the speedo readings manually. The beauty about this option is i can install it without modifying anything in the car. I dont know what its called but here is a video regarding this device If i can find one that will plug into my speedo sensor ill try this method first.
