The key to "rider satisfaction" while using the Fuel Gauge on the Sprint RS and ST is to understand the design of the fuel sender (also referred to as the fuel level sensor).
First, the tank is sloped and of an irregular shape. The fuel level sensor is mounted into the tank on the back left corner. Due to the mounting location and the shape of the tank, the sensor cannot reach the top of the tank. On your gauge, this translates to 80-100 miles (130-160km) of operation before the gauge moves off of full.
Next, if you notice the shape of the tank you will see that the tank is longer at the upper half of the sender. On your gauge, this translates to a slow drop from full to half a tank and then a more rapid drop from 1/2 to empty.
When the level drops so that there is approximately 8/10th US gallon or 3 litres left, the low fuel level light will illuminate on the dash. This will give you approximately 30-40 miles (45-65km) of travel before running out of fuel.
Capacity of tank is 21 litres (5.5 US Gallons / 4.6 Imperial Gallons)