As for weight measurements, body fat results can vary without the product being faulty. A common reason for a variation in body fat is a variation in body water levels. To extrapolate the percentage of fat, our products first measure the water content. These can vary hugely depending on the time of day, on whether you have been to the bathroom and at different stages of the menstrual cycle. Again, it is not important to note any day-to-day variations but to track changes over time.