Do you mean the charts that come with your scan results? If so, then the charts I have show 3 curved lines and a cross. Along the bottom of the chart should be time in weeks and up the side the measurements. The cross should be where your baby is measuring. The top line shows the upper 95th percentile, the bottom shows the bottom 5th percentile, and the middle line shows the 50th percentile. So if your cross is on the middle line, then your baby measures bang in the middle range of all measurements taken at the corresponding number of weeks. If it's above the top line then baby is in the top 5 percent of measurements for the same number of weeks, if it's below the bottom line, it's in the bottom 5 percent. So the charts show you how you compare to other people measured at the same point in time. Hope that makes sense.