I have been using a Body Fat scale to measure my body fat % over the past few years. These scales are actually not very accurate if you want to get a precise idea of your body fat percentage but they are very helpful if you are interested in observing trends of how your body fat changes with time or changes in your diet or exercise.
Most body fat scales use bioelectrical impedance analysis, which basically means that when you step on such a scale, it sends a small electrical current up through one leg and down the other leg and measures the resistance encountered by the current as it passes through your body. Since the Fat in the body is a poor electrical conductor while muscle is a good electrical conductor, the measured resistance can provide an indication of the relative presence of muscle and fat.
The accuracy of this reading is dependent on several factors such as your body temperature, hydration levels, and even your body type. However, you can increase the reliability or atleast the consistency of the readings so that you can more accurately track your progress by taking the measurements at the same time of the day in a room that's typically at the same temperature level with the same amount of moisture levels on your body (before or after shower, hydration levels, before or after exercise etc.). Just choose a state, time, and location that you works for you and be consistent.
If you are really interested in a more accurate reading of your body fat levels, you can use body fat calipers, or visit a facility that specializes in body fat measurement using DXA (dual energy X-ray absorptiometry) scans or hydrostatic weighing.
Each of the more accurate options are either time consuming or expensive or both, so the convenience of a at-home body fat scale is hard to beat. Afterall, unless you are a pro-level bodybuilder or elite athlete the numbers themselves make little sense, it's the gain or loss that's more important to track.
As an example, below is my body fat % over the past 8 months. You can see that it was holding steady until about March of this year at which it started dropping precipitously.
Overall its a drop of 1.5 points which is equivalent to a loss of 12% in bodyfat. I also lost 14.8 lbs. of weight during these two months.
Now, this is not something that I really needed to do as I was happy with my weight and body fat % where it was before. I had been able to hold that weight pretty constant over the past few years thanks to the principles I talk about in the ABCD method. The changes that I made in the past couple months were driven by part curiosity and part experimentation and partly just a desire to see how far can I push it while being away from my regular workout routine. They were actually very small changes and I can summarize them as follows: Calorie deficit in addition to Intermittent Fasting, breaking fast with liquid meal with protein, fasted cardio on few days, daily walks, exercises 5 days a week spread throughout the day. These small changes were selected to help my body adapt to the reduced volume and frequency of workouts I was doing with the gyms being closed and my new routine. And the effects were noticeable from the first week.
Many people keep waiting for some magic diets and workout regimen while the solution to their weight and health problems are right in front of them. They swing from one diet to another and hope that they can find something that finally gives them the results they want, while ignoring the basic principles of health & fitness. The fix is easy. Let's get back to the science and follow the basics. Results will come.