Speedo calibrator by Dakota Digital. Used to correct speedometer when changing tires and/or drive ratio. The unit plugs directly between the stock Harley transmission sensor and the original speedometer or ECM and is easily tucked away into the bike''s wiring harness after adjustment is complete. Ability to correct the speed to within 1 MPH or KPH with adjustment range of 25% to 400% (see note). Sealed completely from water; dust; and dirt. Note: Later models (04-22 XL; 06-17 Dyna and 2007-up Softail and Touring models) require hardwiring into stock harness; speed correction can be made up to Harley''s factory margin of error; typically 3-5% of actual speed reading. If correction is made beyond this; it may result in the loss of the 6th gear indicator light and cruise control.