To answer this we need to understand that there are a lot of factors that cause a person's weight to fluctuate on a day to day basis. Hydration, bowel movements, and the female menstrual cycle are all factors that affect a person's weight. We also need to remember that muscle is more dense than fat and takes up less space, so adding muscle could increase your scale weight even though you're slimming down.

There are better ways of measuring your progress...

Measurements. Taking measurements will give you an idea of where you are losing fat; this is important as we all store and lose fat in different areas of our bodies. 

Progress Photos. A picture can tell a thousand words and is one of the best ways of showing how a person is losing fat or gaining muscle depending on their goal. 

Use your clothes. Choosing some clothes that are a little too tight and then trying them on again four to six weeks later will give you an indication of how you are progressing. Making a note of where they feel loose or where they feel tight and how you feel wearing them will help you track your progress. 

So, whilst bodyweight scales give us an idea of a person's weight, it is important that we don't get obsessed with that number as there are too many other factors that can cause the number to fluctuate. Use the scales AND the other methods above to track your fat loss!