Make no mistake, in the world of philately, when "up" is erroneously "down," value goes up -- way up.

That's why the world's most comprehensive collection of more than 3,000 mistakenly printed upside-down postage stamps owned by the estate of a Mt. Lebanon man is conservatively estimated to fetch more than $4 million at a public auction tomorrow and Friday in New York City.

The collection of the late Robert H. Cunliffe, an investment adviser who died at age 83 in April 2008, includes inverted printed planes, cars, U.S. presidents, landmarks and other designs from the United States and around the world. He began his stamp collecting as a child, first with revenue stamps and, in the 1960s, with the valuable inverts.

"This is nirvana for any stamp auction or collector," said Charles F. Shreve, president of Spink Shreves Galleries, based in Dallas, which is offering the auction at its New York gallery. "This is the pinnacle of excitement for a collector. To see a collection of this magnitude, with inverted stamps from all over the world, is unheard of."

Some stamps mistakenly depict upside-down trains, airplanes, buildings or animals. There also are dozens of upside-down political and historical figures, such as George Washington, Abraham Lincoln and Queen Victoria.

The errors occurred when different elements and colors were separately printed, and a sheet of stamps went into the printing press the wrong way during one of its multiple press runs.

Mr. Cunliffe, a decorated World War II pilot, had been collecting for so long that some of the stamps he purchased for $500 will bring $50,000 or more at auction, Mr. Shreve said.

"Some people have been waiting a lifetime for these stamps to make an appearance on the market. Most collectors are content to have one or two of these [inverts] but he has thousands of them.

"To see a collection like this is beyond comparison. It's like having 1,000 Babe Ruth autographed baseballs in one sale. I'm honored to be able to handle the sale but sorry he's not around for it."

Mr. Cunliffe hired Spink Shreves to auction his revenue stamp collection last year but died before the auction catalogue was printed, said Mr. Shreve, who through philately became a lifelong friend of Mr. Cunliffe. That auction, last June, brought about $2 million.

Mr. Shreve said this auction of inverts is among the top five his gallery has handled, having done others for the Smithsonian National Postal Museum, the Queen of England and for renowned bond fund manager and stamp collector Bill Gross, who donated the proceeds of his $10 million auction to Doctors Without Borders.

"It is a legendary collection," he said. "This collection really gets collectors' hearts racing. "

And not just here. The gallery has received inquiries about the auction from Australia, India, the United Kingdom and Russia, among other countries, Mr. Shreve said. The collection was displayed in Dallas, London and Paris earlier this month. Because the auction also will be operated in real time via the Internet, bids are anticipated from around the world.

Mr. Cunliffe, who was passionate about collecting, loved the camaraderie of fellow philatelists, traveling the world to appear at courts of honor at various stamp collecting conclaves, one of which was sponsored by Prince Ranier of Monaco, Mr. Shreve said.

The collection includes an example of the world famous "Inverted Jenny," a 1918 24-cent denomination airmail stamp with an upside down Curtis JN-4 -- "Jenny" -- biplane that is expected to sell for approximately $100,000 to $150,000.

Five examples of the so-called "C.I.A. invert" stamps also will be offered in the auction: a single stamp valued at $21,000 and a block of four that's expected to sell for $84,000 or more. According to Spink Shreves, the printing error is named for the circumstances of its discovery in 1979 when several CIA employees purchased a sheet of $1 denomination stamps from a McLean, Va., post office for use on agency mail.

When they noticed the upside-down printed central design, a Colonial-era candle lamp, the employees sold most of the stamps to a dealer. CIA officials tried for years to get them back, claiming they were CIA property, but lost their case in court.

Mr. Shreve said he's so excited about the auction he likely won't sleep tonight -- a minor downside of being so up.