The scale has seperate platforms for your three (truck front and rear, and trailer) axles.
First pass- pull onto the scales with truck front axle on one platform, truck rear axle on second platform, and trailer axles on the third platform. This is with trailer hitched up like your going on the road. Then pull off the scales and remove the weight distribution bars.
Second pass - Pull onto scales same as first pass. Then pull into the parking lot and unhitch the trailer.
Third pass - Truck alone, pull onto scales with front and rear axles on platforms one and two. Pay for weight tickets, hitch up and go home.
Some scales will allow you to stay on the scales for all three weighs, others prefer you pull off and back on. Check with scale personnel (before you weigh) to see how they would like to proceed.
What you need is:
Axle weights of truck and trailer hitched up with wd bars installed and set for travel.
Axle weights of truck and trailer hitched up without wd bars
Axle weights of truck alone (remove the hitch)