When properly adjusted, the rim portion of a bicycle wheel is centred perfectly over its hub axle. Centring is determined by tension on the hub from opposing spokes. In "dishing" a rear wheel, one side of the wheel is measured against the other to judge whether the rim is centred or not. Dishing can be performed with the wheel on or off the bicycle. Removing the wheel first, however, allows the dishing tool and wheel to be more easily manoeuvred.
Place the block on each foot of the dishing tool against the side of the rim of the wheel.
Lower the sliding gauge in the middle of the dishing tool against the surface of the wheel's axle locknut. The locknut is located just to the inside of the tip of the axle.
Turn the wheel over. Place the dishing tool blocks against the side of the rim, and note the position of the sliding gauge in regard to the axle nut. The wheel is balanced if the sliding gauge is touching the surface of the axle locknut, as it did the first axle locknut. The wheel is not centred if the sliding gauge falls short of or exceeds the surface of the locknut.
Determine which set of spokes needs to be tightened to centre the wheel. Spokes run alongside both sides of the wheel. If the sliding gauge fell short of the surface of the second locknut, the spokes on the right, drive side of the wheel need to be tightened. If the sliding gauge exceeded the surface of the second locknut, the spokes on the left, non-drive side of the wheel need to be tightened.
Use a spoke wrench and give each of the spoke nipples on the proper side of the wheel a one-quarter counterclockwise turn. The "nipple" attaches the spoke to the rim). Turning the nipple counterclockwise against the spoke adds tension to the spoke.
Use the dishing tool to check the adjustment. Continue to add tension to the proper spokes until the wheel is centred. The wheel is centred when the dishing gauge touches both axle locknut at the same spot.