In order to graphically and orderly present each possible output from a
logic gate or any digital circuit, a truth table is used. These tables
present every possible combination of input states and its corresponding
output.
The first columns represent each of the input variables, and the last
one (or few if there's more than one) represent the output of the
circuit. For low number of variables (lower than 4 or 5) the number of
possible combinations is small enough to be able to represent in a truth
table, and all possible input combinations and their corresponding
output can be quickly visualized
