Fuel Gauges on 737

Can anybody clue me in out there? I will be flying a 737 for a virtual airline , and included with that will be fuel usage reports I would imagine.
I downloaded the plane, and when it is sitting full on the runway the left and right fuel gauges both read 10 3 (the three is smaller than the other two numbers) then below that it is posted (x 1000).

Maximum fuel capacity for the aircraft is listed as 35,233.30 lbs. or
5259.61 gallons. Plus there is a center tank........so what in the world am I looking at on the fuel gauges? Pounds? Gallons? Liters? or None of the above?

I checked the Learning Center on the FLight Simulator and everything else on there I could think of, and have come up with no explanations on this. Are the gauges giving me percentages of full tank or what ? 😳