In 1905, Albert Einstein published his theory of special relativity, teaching the world that time is relative.

In the science fiction novel “The Hitchhiker’s Guide to the Galaxy,” author Douglas Adams declared that “Time is an illusion, lunchtime doubly so.” And in March of every year, Daylight Savings Time begins, reminding us again that time isn’t absolute as we set our clocks ahead an hour.

Historically, there have been many ways to track time and account for the changes in daylight hours that come with the seasons. In some systems, the length of an hour could vary with the time of the year. In 19th-century Japan, stick clocks kept track of days and nights, each divided into six units called “toki.”

In spring and summer, a day toki lasts longer than a night toki, with the opposite in fall and winter. Clocks, therefore, had to be adjustable. Some had interchangeable front plates that could be removed and replaced at different times of the year. Others, like this one, which sold for $5,700 at Cottone Auctions, marked the toki with sliding plates. To a casual viewer, the set of thirteen plates down the front of the clock may not be as noticeable as the pierced scrolls and painted flowers and patterns that decorate it. A close look would show that those plates are numbered, and what’s more, they are not evenly spaced.

Q: How can I tell if my Tiffany’s lampshade is, in fact, an original?

A: Louis Comfort Tiffany’s lamps are some of the most famous and desirable pieces in American decorative arts, and they sell for high prices. Unfortunately, this also means that there are many reproductions and forgeries on the market. There are a few ways to check to see if your lampshade is authentic Tiffany. First, check the metal parts for a mark. Authentic Tiffany lamps are marked “L.C. Tiffany” or “L.C.T.” in capital letters. Check for materials like zinc, resin, painted glass, or plastic; you would never see them in an authentic Tiffany lamp. Take a close look at the glass. Authentic Tiffany glass will have tiny specks of color, called confetti glass. Gold-colored glass will have a translucent amber sheen. Fakes or reproductions will have a silver or greenish sheen. Remember that reproduction and “Tiffany-style” lamps can still sell for high prices.

Q: I have a Princess Diana Beanie Baby. Is it worth more now? Are you able to see how much I can sell it for?

A: There is still a resale market for Beanie Babies, although prices are not as high as they were in the 1990s. Princess, the bear designed in honor of Princess Diana, is popular among Beanie Babies collectors and royal enthusiasts. Contrary to popular belief, it was not a limited edition. Proceeds of the original sales would be donated to the Princess Diana Memorial Fund, so the company could not start making the toys without approval from the fund’s managers. They received approval on Oct. 29, 1997. The company wanted the toy in stores in time for Christmas, so they had to limit production. Later shipments had greater production.

The Princess bear was retired in 1999. According to tycollector.com, a Princess bear can be worth $7 to $175, depending on its condition and tags. We have seen them sell at auctions for anywhere from $24 to $120. If you search for Beanie Babies on eBay, you may see much higher prices, but be careful. Those are the prices the seller is asking for; not what buyers will pay. Search for “Sold Items” under Advanced Search to see real sold prices.

TIP: A damaged porcelain clock face is difficult to repair. It will lower the price of a clock by 20 to 30 percent.

EDITOR’S NOTE: Terry Kovel and Kim Kovel answer readers’ questions sent to the column. Send a letter with one question describing the size, material (glass, pottery) and what you know about the item. Include only two pictures, the object and a closeup of any marks or damage. Be sure your name and return address are included. By sending a question, you give full permission for use in any Kovel product. Names, addresses or email addresses will not be published. We do not guarantee the return of photographs, but if a stamped envelope is included, we will try. Questions that are answered will appear in Kovels Publications. Write to Kovels, King Features Syndicate, 628 Virginia Dr., Orlando, FL 32803 or email us at collectorsgallery@kovels.com.