You will be surpriised to know it's accuraxy is quite good and it's beeing used. This is the plan B when there is a total or parcial (individual tank) failure of Fuel Quantity Indicating System. Also when system loss is accurracy. It is a method that allow airplane dispatch for several days w/o disrupting service, till a permanet repair is made.
There are several sticks in each tank, enough to have differents fuel distribution covered. Now they are located in the lower wing surface. Long time ago, there were "wet" sticks, (B707...) you lowered the stick till fuel start flowing from a perpendicular to the stick orifice.
Now they are called "Dry". There is a sealed cilinder inside the tank, in the outside, wet, part of the cylinder there is a magnet attached to a float who move up and down following fuel level in this part of tank, when stick is released from flight all the way up/lock position, it moves inside the cylinder and stop there where iron tip on the top of the stiick is fixed by magnet, this is the actual scale reading. Manufacturer calibrates the sticks and determine which ones should be used in dependance of requiered fuel configuration.
The reading is corrected in dependence of aircraft pitch and roll parked angle and, by calculation, to actual fuel density..
Pitch and roll may be taken from physical inclinometers located in most of the planes in main landing gear bay., or, in modern a/c, from the inertial system reading on the onboard display unit. And finally, in the MD11 you enter the drip sticks readings in the FMC 's Display Unitt, the fuel density value and the computer makes the whole calculation .