Fuel Gauge question

[Blue_Neon]

My fuel gauge seems to go down VERY quickly, like it can move from 1/4 full to empty in 3-4 miles

I guess I have lived with it since I bought it, but am noticing it much more latley. I put £10 of gas in it (say its 10 liters or 2 ish gallons) when it appeard to be empty, the needle moved up to 1/4, I drove 30 miles not thrashing it (i rarely do) and its now registering empty.

I checked the resistance of the sender, it read 48.1 ohms, book says the following:

Float Position Resistance
Full approx 4-6 ohms
1/2 approx 30-35 ohms
Empty approx 80-90 ohms

So the needle SHOULD read approx just over the 1/4 mark with my reading of 48.1 ohms.

I am not sure what to do, is the gauge notoriously lazy? can the gauge be changed so I can test it?

Also the 'low fuel' light, I have never run the silvia out of fuel. The light comes on when i put in the key (so I know the bulb is ok!) but immediatly goes out when the car starts. I have never seen the light come on, this is possibly because the fuel gauge is so far out that I have kept it well topped up with gas, and never let it hit the low mark.

Is there a way to test the Light (sender?) is working (without running the car dry)

ANY thoughts would be great, does anyone have a spare gauge I can try?

Thanks

T