Calibrated sight gage with LED illumination. This really does help identify the fuel level. FYI: 6 gal to the bottom of the lower P-Clip, 7 gal to the top of the P-Clip, 8 gal to the 1st white tie, 9 gal to the 2nd tie, 10 gal to the 1st black tie, 12 gal to the 3rd white tie, 14 gal to the 4th tie, 16 gal to the 5th tie, 18 gal to the 2nd black tie & 20 gal to the top of the upper P-Clip.