Now I know why you are so busy
smash made a tiny mistake: the beakers given when you scratch specialists and set science to zero are those needed for the tech , not those left to research.
About measuring how much is left, IMO it is boring and not needed to keep a tally (except if you are playing OCC). You can use the slider on top of your science window: it is very precise, except in the very early game.
Much more important is the 'reference civ' discovered by samson:
There is a ranking of civs, from white (for example Romans) to purple (for example Sioux). There is also a ranking for power, from supreme to desperate.
If you are supreme (#1), your reference (target) civ is purple (#7) If you are #2 (mighty ?), your reference civ is #6 (weak ?)... and so on.
Now when you give your techs to your reference civ, this lowers the number of beakers needed for researching the next one (until you reach the minimum which can also be calculated, but I am too lazy to explain just now).