I have made up a dip stick for my J160 by totally draining the tanks then adding 10 litres at a time, marking dip stick until full.
Works very well but as Brentc mentioned the tanks are very flat so is only accurate on level ground - although it is not such a big problem. For example if the aircraft is level with 25L a side, it may show 0 on one side and 50L on the other when on a slope.
Because I made the dipstick, and know how it works I can confidently fly with the gauges touching the red. Did not feel comfortable doing this without the dipstick.
Does anyone know why Jabiru don't supply one?