Bingo, came in to throw my two cents out as a driver. Only difference between the OP and trucks is that trucks typically measure the pressure in the suspension (virtually all trucks built in the last 20 years use air suspension, at least for the rear axles), which gives a surprisingly accurate reading.
Most of the trucks I've driven have either an analog "rear suspension pressure" gauge, or a digital calculation of approximately how much weight is there for the given pressure. With an analog gauge, you as a driver start to get a better idea of how much weight is on your drives, possibly saving yourself from shelling out $20 to scale up on a regular basis. As I sit in my truck without a trailer, I currently have a reading of ~10psi; this truck for instance, every additional ~5k lbs over the drives is an additional ~10 psi in the bags.
Most of the trucks I've driven have either an analog "rear suspension pressure" gauge, or a digital calculation of approximately how much weight is there for the given pressure. With an analog gauge, you as a driver start to get a better idea of how much weight is on your drives, possibly saving yourself from shelling out $20 to scale up on a regular basis. As I sit in my truck without a trailer, I currently have a reading of ~10psi; this truck for instance, every additional ~5k lbs over the drives is an additional ~10 psi in the bags.