Interesting gauge....

Yes, that's what it is. You make notes as you gather scale weight tickets and compare them to the corresponding PSI. After a while you learn where your legal limit is in terms of PSI in the air bag system.

There are a few different gauges and systems that end up at the same place, such as digital PSI readouts, or "weight" readouts [after calibration] such as

 

You won't know until you load it. No two are the same. Every truck is different. Also depends somewhat on fifth wheel placement also in relation to steer axle.
Your drives may be good but the steer will vary with fifth wheel placement.

 

Put a load on and then scale it. My guage says 62 pounds is 34,000 on the drives.

 

With truck air ride systems, the PSI required to maintain a set height will always increase/decrease proportionally, as the weight changes. Furthermore, any lessening of weight at point A, requires an identical increase in weight somewhere else. In the case of drives/steers only a shift of the 5th wheel can change to ratio between drive and steer weight changes. Ideally, once a "sweet spot" is found for the 5th wheel, it should never be moved again ... getting to the maximum on the drives will always put you where you're ideally weighted on the steers.

Then it's just a matter of getting a good weight balance between the trailer and tractor by means of moving the trailer tandems. If a trailer gets lighter by 1,000 pounds after a trailer tandem shift, then you know 1,000 pounds has been added to the tractor (and that weight was distributed between the drives and steer according to the ratio as set forth by the position of the 5th wheel on the tractor ... might have increased the drives 900 pounds and the steer 100 pounds)

 

Also, with air bag systems, for all intents and purposes, the PSI:weight numbers should never change. Changes in barometric pressure and or temperature can make subtle differences, but these are generally too minor to consider. Changing out air bag(s) or changing the ride height is about the only thing that will require the user to gather new data to establish a new base-line for PSI_weight (recalibrate)

I have had an air-weigh system to become "mis-calibrated" for as much as 900 pounds, for a still unknown reason.

Furthermore, air bags have a tendency to require "settling in" before you can truly trust the PSI reading. After loading and recharging the air bag systems, I prefer to move (bounce) around the parking lot a bit before finding a level spot to check weight (PSI)

 

On my 579 Pete 70 psi is 34000, I usually do the same as @STexan. Once loaded, I cruise the parking lot, and then double check rolling down the highway.

 

Seeing as it is not even registering 10 psi if you were bobtail I am thinking it is an air application gauge .... does it show a reading when you apply the brake?

Edit: thought you were asking about the top gauge. the bottom one does look like a 5th wheel psi gauge. Like everyone else said usually 60 or 70 psi will be 34000 on your drives.

 

Use this to also judge weight on the tandems. If a dock loads you up near your known max, and that guage shows you under max on the drives, you are likely tail heavy and need to slide the tandems back a few holes.