(FORTUNE Magazine) – The pleasing, buttery feel of manual shifting that motor buffs crave in an agile car. The welcoming contours of a power-tool handle. The sensuous blend of fluidity and resistance in the focusing knob on a pair of binoculars. These and more are the details of machines that are great to use because they fall naturally to hand and feel logical and right.

Devices so inviting don't just spring into existence. They result from the patient work of largely unsung specialists known as human-factors engineers. Also called ergonomists, these experts know the sizes and shapes people come in, how they can and can't move, how they acquire and digest information, and how machines can be shaped to accommodate them. Human-factors engineering originated in World War II, when the U.S. and British military wanted to know, among other things, how many sizes of gas masks were needed to fit the troops.

To this day, sad to tell, human factors are widely ignored or executed badly in product design. Think of VCRs with hard-to-understand timers. At the extreme end of the failure spectrum are catastrophes: the reactor meltdown at Three Mile Island, caused in part by hard-to-interpret control-room displays.

But smart companies have been cashing in on the latest human-factors wisdom with products like these:

Schlumberger's new way to "complete" an oil well. The Dowell division of Schlumberger Ltd. in Sugar Land, Texas, provides services to oil and gas drilling companies around the world. Many of its jobs at well sites involve heavy equipment called a coil-tubing unit. Dowell has a new version called CT Express, shown on these pages, that takes a lot of the complexity--and hazard--out of the work.

One job of a coil-tubing unit is to "complete" a well, as the roughnecks say. Once the well is drilled and lined with steel casing, a large volume of drilling "mud" must be removed before the well can produce oil or gas. The coil-tubing machinery includes a 10,000-foot reel of flexible, narrow-diameter steel pipe that is stuffed down the hole by a device called an injector head. To drive the mud up and out of the hole, nitrogen gas is pumped down the pipe.

The scene at a traditional well completion has a Wild West flavor to it. Four major vehicles collectively worth nearly $3 million are involved, whose four operators communicate with each other and their supervisor by walkie-talkie. Keeping a close watch on the injector head is critical. If the tension is wrong and the device loses its grip, the tubing can go shrieking down the hole, and perhaps rip the reel off the truck as well. When underground pressure is high, on the other hand, the tubing can come spitting out of the hole like satanic spaghetti, spraying corrosive acid propelled by pressurized nitrogen. If this starts to happen and countermeasures don't work, says a Dowell engineer, "it is time to run like hell."

The new CT Express costs only $1.5 million, fits on two stately orange Peterbilt trailer trucks, and needs only three operators. One person is in charge of it all. Housed in a booth that is heated in winter and air-conditioned in summer, he sits in an ergonomically designed chair equipped with integrated keypads and fighter-plane-style control sticks. A pair of large flat-screen displays shows the functioning of various subsystems in an iconic fashion that's easy to grasp.

The injector head is largely controlled by sensors that automatically detect slippage by comparing pipe speed with gripper speed, making any needed correction and alerting the operator. Says Dowell's Terry McCafferty, head of the team that developed CT Express: "We want the operator to be able to focus more on the mission and not on the individual devices." Dowell plans to order about 25 more of the units from its equipment supplier, Hydra Rig of Fort Worth, as soon as it gets feedback from users of two prototypes.

Cool lift trucks from Crown Equipment. At the start of a shift, it's widely said, warehouse workers sprint to be the one who gets to spend the day aboard a machine made by Crown Equipment Corp. of New Bremen, Ohio; that's how slick they are to use. Crown attracted praise in the '70s with the introduction of a counterbalanced lift truck on which the operator stands sideways instead of facing in the direction of travel.

The inspiration came from paying attention to human factors. A designer observing the machines then in use was bothered to see operators driving down narrow warehouse aisles facing forward, and then reversing the journey by turning around so they could see where they were going and working the controls behind their backs. Crown's new "side stance" layout allowed an operator to see either way by simply turning his head.

For its latest generation of side-stance truck, the RR 5000S, Crown devised a flip-up seat and extra pedals that allow the operator to relieve body fatigue during the workday by varying his posture from sitting to leaning slightly back to standing. The controls are within easy reach to keep the operator's body stable, with hands and feet firmly planted to minimize his chance of falling off while whipping around corners.

DaimlerChrysler's driver-friendly vehicles. Though competing makes have crowded in, DaimlerChrysler has hung on to a 45% share of the U.S. minivan market by drawing on a rich body of knowledge about drivers' dimensions, physical and cognitive capabilities, and lifestyles. The company extends driver-friendliness to its cars; one future product it is willing to talk about is the 2000 model year Neon subcompact, which it has displayed in prototype on the auto-show circuit.

Complaints prompted some of the Neon's ergonomic changes. Shorter owners groused about bumping their arms on the seat cushion while lowering the window with a manual crank. Engineers built a test jig with a movable window crank, and measured the preferences of people of widely varying stature. Now they know the crank pivot point that will satisfy 95% of the population, which is two inches higher than in the current model.

Maytag's easy-loading washer. With gasoline selling for less than bottled water, it might seem that Americans no longer care about energy conservation. The strong demand for the high-efficiency Neptune clothes washer from Maytag Appliances of Newton, Iowa, indicates otherwise. The Neptune, which lists at a relatively high $1,099, was a hit from the moment it reached showrooms in 1997. It's easy to use and can save as much as 38% on water usage and 56% on electric bills.

That combination of attributes is missing in the top-loading washers Americans have traditionally preferred. While easy to load and unload, these machines need a relatively large amount of water to get the clothes clean. Front-loading machines with a horizontal-axis drum, popular in Europe, are more efficient. But they're almost impossible to sell in the U.S. because people don't like bending or kneeling to reach the low door.

The Neptune's design is one of those happy compromises that seem obvious after someone else has thought of it. To achieve the efficiency of a front loader but improve access, the designers tilted the washer's drum axis upward 15 degrees from the horizontal. And they devised a door that runs up the machine's front and slopes back along the top to create a large opening. The Neptune's user can load it without aggravating those creaky knees.