Periodically, without anyone taking much notice, the universe makes subtle but eternal adjustments in its operating system. A planet enlarges its orbit, a sun fizzles out, a galaxy turns over on its side, Hobart sells its domestic appliance line to Whirlpool.

Hobart, until a bit over a year ago, manufactured and sold kitchen appliances for both professional and home cooks. The line for home cooks was called KitchenAid, and it included the nearest thing to sacred icon that exists in the world of kitchen equipment.

The KitchenAid mixer, whose visual attributes include a certain clunkiness of form and a minimalist approach to graphics (speeds are called "1," "2," "3," for example, instead of "this speed is for when you want to mash potatoes, and this one is for when you want to mix up cookie batter and this one is for when you want to whip egg whites and this one ... "), is an object of reverence to people who cook a lot. It's strong, brave, hard-working. It never talks back in fake-sincere computerspeak, and it doesn't batter the eye with flashing lights. It just mixes, and mixes and mixes. Then you bequeath it to your children and it mixes some more.

So when Hobart let its domestic line go to Whirlpool (the company kept control of its commercial line, where the serious money is) fear was loosed on the land. The transfer took place with so little fanfare that even some store personnel are just now realizing it happened. The name didn't change, nor did the way the product is marketed. Not even the latest literature carries the Whirlpool name, and neither does the machine itself.

All of which would lead you to believe that Whirlpool would prefer that you keep right on thinking in terms of KitchenAid. And that makes the paranoid among us sit up and take notice.

Happily, there have been only a few changes in the mixer, and they are either harmless (color) or an improvement (more power in certain models).

Here's how things stand:

The top-of-the-line model, most recently called the K5SS but often still known as the K5A -- its former name -- is still basically the same, except that instead of 300 watts of power it now carries 325 watts. It still is the KitchenAid with the biggest capacity in both bowl (five quarts) and motor, and it is a formidable machine.

And it now has begun to appear in a rather shocking cobalt blue, as well as regulation white. Almond is said to be available as well, though I've never actually seen one of this species.

The K5 models vary only in color; power and operating mechanisms in each are exactly the same. The bowl moves up and down -- down when you want to remove it, up when it's in operation -- and the head of the mixer stays stationary.

List price for the K5 models is either $379.95 or $389.95, depending on color, but you should never pay that much. The machines are widely discounted, even in regulation kitchenware and appliance stores. They are also available from some discount houses.

Now things begin to get a bit complicated.

Previously, your choices in KitchenAid mixer were two. You could choose the K5 model, or the K45 model. The K45 model had a 4 1/2-quart bowl (versus 5 quarts) and 250 watts of power. Instead of a bowl that goes up and down, the K45's head moves -- it tilts up and back. That's the way you remove the beaters. The bowl looks slightly different from the K5's, but other than that the two models looked nearly identical.

All those characteristics obtain. The K45 model exists unchanged.

However, Whirlpool has added another model to its line. It is called the "Ultra Power" model (technically two models since it comes in two different colors), and the only important way in which it differs from the classical K45 is that it has 20 percent more power -- 300 watts instead of 250. So what you've got here is a machine with the configuration of the old K45 and the power of the old K5.

And that seems like a pretty good combination.

What you get when you get more power is the ability to mix stiff batters such as that for bread dough or pie crust without taxing the machine. When the machine can't handle its burden it either skips along the counter or overheats or both.

With 300 watts of power you can safely mix at one time enough bread dough for three regular-sized loaves of bread. The regular K45, at 250 watts, has the capacity to do that also, but it will have to work harder -- it may slow down, start moving across the counter, or get very hot. The more power you have the better mixture you'll get, and the quicker you'll get it.

And many cooks, after they've worked with the tilt-back head a while, begin to prefer that to the stationary head. With the tilted-back head it's easier to see what's going on in the bowl and to get at what's in there when you need to do a bit of hand mixing, scraping down of sides or adding of certain ingredients.

What difference does half a quart make when you're talking about bowl capacity? KitchenAid home economist Tara Widener notes that company-issued recipes for both the 4 1/2-quart models and the 5-quart models are identical. In other words most home cooks wouldn't notice the difference. Widener also says the company is aware that many cooks will exceed the listed quantities in any case.

Cooks who prefer the extra capacity are mostly those who make lots of billowy things such as meringues, meringue-based frostings or whipped cream, Widener says.

And here's a bit more information to help you make up your mind: the 300-watt, 4 1/2-quart mixers cost about $100 less than the 325-watt, 5-quart model. With discounts you should be able to get the former for not much over $200.

Since there's not much practical difference between 300 and 325 watts, and since chances are that a half-quart difference in bowl capacity won't matter much either, and since all the attachments available for one are available for the other, it makes sense to think carefully about whether you prefer the tilting head or the up-and-down bowl.

As for the old K45 model, which is still being produced, it's hard to understand why anybody would buy a machine that has about 1/6 less power than the new powered-up models but costs only about $10 less.