More accurate gas tank readings

'Member one time I was goin' somewhere in my 70RR. Those have the filler low, behind the plate. I dove off I5N, filled up, and the ramp back N was nice and straight, so I got right with it. Ran up the road about a mile, and here we have less than a 1/2 tank. Had the trunk open, checking the oil, and had laid the cap in the trunk, then forgotten it. Boy it didn't take long to sheeeitt a lot of gas right out the rear.