How acccurate was the weight prediction you were given at a scan?

Sometimes it can be wrong. With my third son I was told he was going to be over 10lb and he was only 7lb 10oz when he was born. I asked why and was told it was because of the length of his legs. They measure from the hip to the knee, then down to the ankle and based on the length, the computer then gives an estimated weight. My son was 64cm long in total. This was the explanation I was given when I asked. I hope I haven't confused you!! lol