A unit (as one loaf of bread, one coconut, one cookie, one fish, one cup, one house, etc.. This is almost always used when enumerating an amount of units that aren't sufficient).
If you're just giving two little sponge cakes, how will I get full?
To get a whole unit; to break things down to their specific units (as one by one when telling s.o. the names and ages of all their relatives, or as when giving all the specific details about a boat that is seen from a distance).
I'm surprised at that person because he can tell one by one the names of everyone in our family.
He can't afford to buy a whole fish because he's short of money.