Your fuel tank is L shaped. So by now you have figured out that the guage is linear based on the fluid level on the rod.
Thus you have a based adjustment for the empty, and a gain adjustment for full. Hopefully your site tube is on the same side as your fuel guage.
Determine what you want to call empty (ie 2 gallons). Fill to two gallons (I have a T between the two sides) and set your base (empty). You can do it several ways from here.
You could fill to 10 gallons and set the gain (full adjment) so you reads 1/2 tank as it will be over the hump with 10 gallons. Or you could fill the tank and set it at full. Ron Menzie starts out lessons with 10 gallons and is down to 5 gallons at the end of an hour.
Now you can empty the tank. Add two gallons at a time and mark you dash guage with thin colored plastic tape. If you use the 10 gallon method your guage will read full for a long time if you fill the gyro. But most people do not fly with more than 15 gallons. Never - ever trust a guage. Know your general burn rate and carry a stop watch. Check the site tube each time you land so you have a rough idea of your burn rate and if your guage is set correctly. Thus if the watch and guage do not jive in flight you know roughly what you have left.
I appreciate your thoughts. What I'm looking for is the instructions for using the RAF gauge. Mine has several holes in it with LED lights in each hole. At the bottom of the gauge is two holes that you push a small wire or pen that sets the top and bottom level or I have been told, you can set each level as you start from empty and add X-gallons at a time. I've messed around with mine and cant figure it out. Any thoughts?
Curt, my RAF tank is shaped like a pair of saddle bags and sets over my keel, the fuel is added to the tank only on one side of the saddle, when you put fuel into this one side, you must have a cross over line from one outlet line to the other or the fuel would never seek its own level, once you add, say 5 GAL to this one side, you must wait until the fuel seeks its own level before you push the left or low limit button. if you do give it enough time to seek its own level then the side where you added the fuel will now only have 2.5 gal. in that side of the tank, and that is ok because when that red low limit light comes on you still know you have 5 gal. total fuel left in your tank.
Curt, that is the same gage i have, using the information i printed above, for your minimum amount of fuel, now put in another 10-15 gal. and push the right button (i used a tooth pick) to set the high limit of full mark. if you put in more than 10-15 gal, the light will just stay on until it gets back down to the 10-15 gal. by doing the calibration this way, the full light will just stay on longer than if you set the high limit with, say 20 gal.