Not as such no. I rely on the computer. The check light has just come back on and I've noticed that when I push the O/D button, it does not come up on the display. I guess this is what the mechanic saying the gears are not correctly working is about. A little concerning. Things just go from bad to worse with this vehicle.
You need to calculate by hand, the computer can often times be inaccurate. Till then, we don't know what mpg you are truly getting.
I noticed that when i ran 87 octane (Unleaded fuel) my rx got terrible gas mileage so what i did i change my spark plugs with some ol' ngk irdum ones (old ones looked like they just about had it verry crusty and rusty and brown) cleaned my maf sensor (was extreamly dirty) changed my air filter (that thing looked like crap) then ran a can of sea foam through my engine, changed my oil got a filter and gasket for my transmission (trans oil was black smelled a tad burnt) went to the gas station to fill up on some good 93 octane (premium fuel) got 14 - 19.4 in the city and 24.5 on the freeway also noticed my transmission shifted smooth as silk and didn't drag anymore and on my rx300 i have about 175,000 on her clock