For those asking how LPG vendor calculates how much LPG he's putting inside your car;
They usually have those tall 5' Cylinders, they contain approx. 55 KG LPG inside them.
They have a Digital scale, they place the LPG cylinder upside down, note the weight. I.e it shows 30 KG on the scale, then he will Zero/ Reset the scale and start the pump. The values on the Digital scale will be at 0 then. When LPG starts to fill inside your cylinder, values will start going in negative. I.e, he filled 4.5 KG- Value on Scale: -4.5 KG. So, you know how much to pay.
Know what? I'll try to make a video tomorrow, where they fill LPG in CNG cylinders in a Hiace. Good han?
Most of your queries will be explained, including a start up video.