When your mood is up and your dress size is down, it’s easy to believe in your bathroom scale. Then comes a rough week, and instantly your scale morphs from ally to accuser. With friends like that, you think, who needs fashion mags to feel fat? The truth: No matter what it says, a scale can help you shed pounds you don’t want. And for dieters, it’s just one of many supportive friends. Here’s how to make those friendships pay off.

Put your scale to work—early and often
Researchers at Brown and Duke universities recently found that 61 percent of people who climbed on the scale daily maintained their weight within 5 pounds. Only 32 percent who weighed in less often had similar success. Regular feedback helps catch weight gains early, explains Daniel C. Stettner, PhD, a health psychologist at the UnaSource/Northpointe Health Center weight-control clinic in Michigan. Staying accountable to the scale may help you cut back on impulse eating and denial.

For consistent results, weigh yourself at the same time of day and on the same scale (sensitivity can vary between models). Stettner recommends doing it first thing in the morning, after you use the bathroom. Try sticking with weekly or semimonthly weigh-ins if you’re obsessive (that is, if you’re inclined to weigh yourself several times daily) or lose perspective easily (one fluctuation ruins your day). Susan Bowerman, RD, assistant director of the University of California, Los Angeles, Center for Human Nutrition, favors Friday weigh-ins because they reflect the week’s efforts and help keep you motivated over the weekend.

Which scale is best? One that’s simple and reliable; the reading should be the same when you step on and off three times. Scales that measure your hydration and body mass index usually aren’t reliable. We like the Thinner Soft Step Scale at Bed Bath & Beyond ($39.99; 800-462-3966) and the Health-O-Meter Digital Lithium Scale at Kmart ($34.99; 866-562-7848), which have 10-year warranties.

Chart your progress
Patrick M. O’Neil, PhD, a weight-management expert at the Medical University of South Carolina, likens a person’s weight to the stock market: The numbers rise and fall from day to day, so it’s motivating to see long-term trends at a glance. After overindulging, for instance, you’ll be more inspired to hop back on the low-cal wagon if you can see that the numbers are going down. Print out a graph, mark it each time you weigh in, and connect the dots to see the trend.

Size up your body
A tape measure is a good choice if you want harder data than “my clothes fit better.” Bowerman recommends measuring your waist, hip, bust, and upper arm every 2 to 3 weeks (it takes several weeks to see changes).

Log your eating habits
Ever grabbed a doughnut (330 calories) in the morning, sipped a mocha latte (340) at work, and munched half a bag of potato chips (600) in the afternoon? Keeping track can help. You’re more likely to curb your habit, in other words, if you know how many lattes you had in the past month. “People don’t realize how often and how much they eat, so a food diary can be a real eye-opener,” O’Neil says. Seeing your eating patterns might even inspire healthier stress relief: Instead of pigging out after your insufferable boss goes on the warpath, maybe next time you can close your door and do healthy stretches.

To track calories and nutrients online, O’Neil recommends mypyramidtracker.gov. Bowerman prefers a simple notebook, because you can record foods immediately rather than having to wait for computer access.

Record portions (“1 cup mac ‘n’ cheese”) and calories, if you’re tracking them. Cutting even 100 calories per day can help you lose weight, says Catherine M. Champagne, PhD, RD, chief of nutritional epidemiology at Louisiana State University’s Pennington Biomedical Research Center. (Click here for a list of 100-calorie foods.) Also note the time, place, emotions, and other eating triggers you experience.

Step lively
Adding 2,000 steps to your day can help anyone shed flab, so strap on a small pedometer and put your feet to work. Just skip the pedometers with bells and whistles. “The only button you need is ‘reset,’” Champagne says. She recommends Accusplits or Digiwalkers, in the $15 range. Attach it to the front of your belt or waistband, lining it up with your kneecap. Wear it for 3 days, and average your steps to find how many you take in a typical day. (Someone who doesn’t exercise much might log 2,000 to 3,000.) Then try to add 2,000 (about a mile) daily. How? Walk at lunch, choose stairs over the elevator, park a few blocks away, walk around an indoor mall, or take folded laundry into the bedroom a few pieces at a time rather than all at once. Work up to 10,000 steps per day, and your scale may just throw you a party.

By Juliet Eastland