Here’s how:
Hold the sending unit outside the tank.
Slide the float assembly up/down on the vertical frame to the position in which it looks like the float will be at the bottom of the tank when there is no gas to float it ( empty tank).
Mark that position on the vertical frame.
Slide float assembly all the way down- that’s the only way to get it into the tank- then wiggly the sending unit into the tank.
Lift the unit, slide float assembly to the adjustment mark and fasten it there.
Lower sending unit into working position and fasten to tank.