I assume you are talking about the checking the Ride Height Adjustment on the Freightliner XC Chassis.
Here is how you check it:
The ride height should be checked at each scheduled maintenance interval. This is every six months or 6,000 miles, whichever comes first. The method for checking the ride height is simple.
Ensure that the coach is on level ground, the air suspension is fully inflated and that you have full air pressure in the air tanks (120 psi on the dash gauges).
Always block the tires to prevent the coach from moving any time you climb under your RV.
For the front suspension on an I-beam axle, slide under the coach behind the front tires. Using a tape measure (butt the tape against the lower flange of the frame rail, do not hook it over the edge), determine the distance from the lower frame rail flange to the center of the lower-shock absorber bolt. This dimension should be 10" +- 1/4".
For the front ride height on an Independent Front Suspension (IFS), measure from the center of the upper shock-absorber bolt to the center of the lower shock-absorber bolt. This dimension should be 17.5" +- 1/4".
On the rear suspension, slide under the coach behind the rear axle. Measure the same way that you did for the front I-Beam axle. The dimension for the rear suspension should be 9-3/4" +- 1/8".