The first time I had my body fat read was when I went for my first personal training session. It was 44%! I weighed 15 and a half stone and am 5'7".
Now that I weigh 13 stone and have been exercising like mad it's gone down to 37% according to the personal trainer's scales. My body fat scales tell me it's 34%.
I think it varies from scale to scale just as weight does. The only way to get a really accurate reading of body fat is with a caliper test.