History of The Weather Channel originally generated only text-based products. Radar imagery was added to the units in June of that year, with graphical backgrounds being introduced in July, making the 4000 the first STAR to be capable of generating graphics and the first to incorporate the channel's logo in the forecast segments. Also in 1990, The Weather Channel began including snow condition reports at five minutes after the hour. Largely considered the height of the classic TWC by enthusiasts, The Weather Channel underwent a major graphical revamp (with the introduction of a new slogan, "Weather You Can Always Turn To") on March 6, 1991.
Proof that π is irrational In 1761, Lambert proved that is irrational by first showing that this continued fraction expansion holds: Then Lambert proved that if "x" is non-zero and rational then this expression must be irrational. Since tan(/4) = 1, it follows that /4 is irrational and therefore that is irrational. A simplification of Lambert's proof is given below. This proof uses the characterization of as the smallest positive number whose half is a zero of the cosine function and it actually proves that is irrational. As in many proofs of irrationality, the argument proceeds by reductio ad absurdum. Consider the sequences ("A") and