I'm sure all you guys have experience with this, when you go uphill, the gas meter is lower, but when you on flat ground, it jumps back up a little, is this normal? which on should I read? cos some times i have like 1/4 tank left, then when I go uphill my gas light would come on.

 

seems normal... just maybe a little more extreme than i am used to. i've had mine drop from a 1/4 of a tank to the red line while rounding a curve or going up a hill. I just havn't had the fuel light come on yet.

 

so if the car is lay on flat ground surface, the gas meter is in the correct reading?

 

this is common. the meter is not extremely accurate. it also goes low when making a right hand turn fast. but a left and it will go up.