Be aware that none of the bio-impedence scales you get (Tanita and the like) are very accurate at all when it comes of calculating body fat %. They are so influenced by hydration that they usually give wildly varying readings.
I would say the only way to use them is
Same Day, Same Time Each Week
Ensure everythign is the same. e.g.. Get up, go to toilet, drink 500ml water, wait 1 hour, then measure.
Even then, all they can really offer is a trend (hopefully in the right direction), the actual number value is pretty arbitrary as it's most likey won't reflect your true body fat %.
Callipers can work, but unless you are well practiced, getting that right is not easy. Many exercise professionals can't even offer reliable measuring.
I personally think that it is often better for people to focus on the measurements with a tape measure. This allows you do see progress in various areas, and get an idea of where the weight/fat loss is coming from.
I use a 9 point measuring system, taken once a week, and entered on a spreadsheet. Heree is an image link to the locations I use