Wikipedia

[Tellos Athenaios]

Obviously one encyclopedia isn't going to cut it for using as the source of all your wisdom and knowledge; no matter what the subject. However; the point I wanted to make was that math, science and electronics are suitable for looking up in encylcopedia (if only for further sources) as these fields focus on established facts and information. History does not; hence an encyclopedia will virtually always be lacking as a source for whatever the historical subject.

For a quick comparison: if you want to know about the difference between DVI-D and HDMI; Wikipedia will be your friend in these confusing HD times.
But if you want to know the political motives for the diplomatic moves of the Tyrannoi of Syrakousai during the 1st Punic War... I wouldn't count on it...