First you might want to check the condition of the walk belt as drag there or in a related area is typically the cause of erratic speeds. The links below and your owners manual have more information on what to check for and how to address those concerns.
Calibration on this model is mostly done to set the correct speed ratio and range for new components and normally will not need an adjustment unless a major component is heavily worn or just replaced. If everything checks out okay with the motor belt, walk belt, and walk platform and the speed still seems off overall then the calibration can be checked as follows:
To enter Calibration mode, press and hold the
and the S
buttons while inserting the safety key.
Level 1 will appear on the console. Press the
button to advance through the levels to Level 2 which is the Speed Calibration.
In Level 2, press and hold the
button (the walk belt will start moving) until the
window displays 85%. At that point you should see the maximum speed in the Speed window (ie: approx 10 MPH should show if you have a 10 MPH max treadmill).
If the max speed is off, adjust the potentiometer on the motor controller until it is correct, or within a few tenths of correct since it can be difficult to get it exact. The adjuster looks like a small screw on the motor control board itself under the hood/cowling.
To exit the Calibration mode just remove the safety key.
Be careful working around the controller and the moving parts both for your own safety and to be sure no damage is done to any of the sensitive components. And make small adjustments to the potentiometer screw as it can be pretty sensitive.
If you have any reservations or concerns you may want to have a professional perform the adjustments for you. Check the "manual" link below to find the owner's manual at Manage My Home or check for it on the manufacturers site at