My 2010 RX 350 has a total of 10 hash marks from Empty to Full. Does that mean each division represents 1/10th of a tank instead of 1/8th?

 

In cars, they call them gauges. Even by Webster's definition, that's exactly what they are, a 'gauge' equal to a guesstimate of what's in the tank. There is a float-valve that sends a signal of how high (in the tank) it is. It's not a precise instrument, never has been. In aircraft they are a little more precise but they still rely on a 'fuel flow' meter that determines how much fuel has come through the line in a given amount of time. Subtracting that from the original volume is a backup 'guesstimate' of what's left. Race cars are judged by the amount of fuel they poured into the tank to top it off after 'x' number of laps. But there is still the variable of speed so...

You guessed it, I've been in the wine again, but the fact is, it's still a gauge. Some are more accurate than others. For whatever reason, most have roughly 1/3 to 1/4 of a tank when they show 1/2 full. Others are more accurate. It varies car to car.

That's my trivia for the night

 

As Cruiter said above, you should guesstimate it.

In RX350, the tank is about 19.2 gal. (72.5 L). When the low fuel warning light is on, you will have about 2.9 gal. (10.9 L) left, more or less. (I don't know if RX has such "reserved tank" stuff)

With your multi-information display, when the low fuel warning light is on, the driving range will only provide you the estimation of 1-2 gal.

(IMO, I don't mean you should always wait to the last moment to fill up your tank, or wait until the driving range = 0. You should do it before/when your warning light is on.)