The watchdog you must pass to see the new show at the Arthur M. Sackler Gallery comes from China near Tibet and is, all in all, just a great dog. His ears are perked and his mind is working.

If you like your dogs fit and wise, and your art excellent, you will agree that this 1,900-year-old mastiff from an Eastern Han dynasty tomb is a most superior animal. His armor is fitted, his sweet doggy face endearing, his patience immense. Unflaggingly observant, he shows you by example how you must approach "Asia in America: Views of Chinese Art From the Indianapolis Museum of Art," the small exhibit that he guards.

No shirking. Pay full attention. Look with care.

Apartment-size -- two rooms and a hallway -- the Sackler's show is no blockbuster, not even close. This show requires work. It doesn't try to wow you. It asks from you, instead, the closest of comparisons. But look hard at what it offers and the Sackler's exhibition will hone the way you see.

Actually, if you don't look hard you'll hardly see it at all.

Two big Chinese platters share a single case. They're nearly identical twins, 500-year-old twins. Try telling them apart.

The platter on the left is a delicate, expensive piece of Ming dynasty porcelain, blue and white and festooned with juicy grapes. So is the one on the right.

The platter on the left, on loan from Indianapolis, has a subtly scalloped rim and displays twisty tendrils. So does its companion, which lives here in the permanent collection of the Freer Gallery of Art. Both platters are oversize, too big for the many-little-dishes style of Chinese banqueting. One of them was made to be exported (packed in straw, on camelback, along the Silk Road's trails) to markets in the West. So was the other. No sensible museum would spend its money buying objects so much alike.

The Indianapolis plate and the Washington plate are almost identical. Almost but not quite.

That "not quite" is what the show's about. Its curator, Jim Robinson of the Indianapolis, says his exhibition "focuses on the differences among similar items." No big thinking is required to detect those differences. That's because they're not big, they're tiny.

A label advises: "Take your time, make lots of observations."

Look again. The platter on the right, the one from the Freer, has better tendrils. They're just better, more graceful, more exuberant. The ones on the Indianapolis platter look too much like the mindless spiral scribbles one sees on notebooks left next to telephones. But they surround better grapes. You know how sweet ripe grapes have a lightly powdered, dusty bloom? You can see it on the grapes in the plate from Indiana. The others, once one has noticed how different they are, start to look like too-blue blobs.

Does this matter? It used to.

Fine museums once encouraged connoisseurship, though nowadays -- as the new National Museum of the American Indian demonstrates -- connoisseurship tends to be rejected as elitist and judgmental, which, indeed, it is.

But, hey, that can't be helped. Anyone who attends lots of football games knows that some wide receivers are better than others. That's not discriminatory snobbery, it's just fact. The same holds for objects. Some are better than the rest. Reaching for the best is one of the key pleasures provided in museums that show great works of art.

Here it's a close call, but if I had to choose between those Chinese platters I think I would select the one housed in the Midwest.

Nearby in another case, which surveys 600 years, are nine tall Chinese jars. Some of them are flowered, others are unpainted, some have slender feet, some fatter, but what matters most among them is harmony of proportion. Study them awhile and I think you will agree that the white one at the left is superior to the others.

Proportion matters mightily when judging Chinese porcelains. So does color. And chemistry -- for when you fire a piece of porcelain, the color that results is minutely dependent on the oxides in the glaze. Add a little iron oxide, just 2 or 3 percent, and you will get a mild green. Add a little more, another 1 percent, say, and your vessels will go brown. This, too, is explored in the Sackler exhibition. So is time.

Together in a case nearby are a pair of antique objects that look a lot alike but aren't alike at all. Both suggest the archaic. There is nothing else they share.

The one at the left was carved of dark, hard nephrite about 4,000 years ago -- why, no one can say. The cong (pronounced tsoong) is a hollow tube, open at the top and open at the bottom, with a squarish silhouette and an empty cylindrical core. Congs are mysterious. Ancient Chinese graves are full of them, but beyond the obvious fact that they stress the rightness of the circle in the square, no one knows precisely what those things were for. The cong-shaped vase that's next to it is not really mysterious at all. It's a flower pot, a stylish piece of Longquan ware made 800 years ago that wants to look antique.

The Sackler and the Freer, which together make up the nation's museum of Asian art, are on the Mall because an industrialist named Charles Lang Freer (1854-1919) was inspired by his friend, the painter James McNeill Whistler, to spend much of his large fortune collecting things from Asia. He wasn't alone. Other rich Americans -- in Kansas City and St. Louis, Chicago and Minneapolis, and, of course, in Indianapolis -- were also buying Asian art.

Hence "Asia in America," a series of exhibitions conceived by Julian Raby, the scholar who directs both the Sackler and the Freer, to showcase the collections of other museums of Asian art. Indianapolis is first.

The Indianapolis Museum of Art owns some 3,000 Chinese objects, many of them purchased by pious Eli Lilly, the pharmaceutical magnate who thought that it would make "our lives more abundant" if we rinsed them in the beauty and "tranquility of spirit" that he sensed in Asian art.

His museum in a garden, founded in 1883 (its 150-acre campus was landscaped by the Olmsteds) is undergoing renovation and expansion, thus permitting this exhibit, which provides this mental workout. Its ancient Chinese objects -- 47 from Indianapolis, eight owned by the Freer -- exercise your eye.

The dog is still there as one departs, still patient and alert. It's a relief to see him. That's because you don't have to compare him with anything else. He's great just as he is.

Views of Chinese Art From the Indianapolis Museum of Art, which inaugurates the Arthur M. Sackler Gallery's "Asia in America" series, will remain at the Sackler, 1050 Independence Ave. SW, through March 20.

Two Ming dynasty platters, the one on the left on loan from Indianapolis, at the Freer Gallery's "Asia in America" exhibition: For museum-goers, an excellent chance to compare notes and tendrils.An earthenware mastiff, above, from the Eastern Han dynasty, serves as guard dog to "Asia in America" at the Sackler. Unlike other artworks in the exhibition, it's not part of a pair meant to be scrutinized for similarities and differences. Left, a cylindrical cong tube from an ancient Chinese grave.