Do not waste your money on them. I've tried them and they are inaccurate as hell.

You will get different readings if:
you are hydrated/dehydrated
Skin dry/callused, or wet/clammy
before or after taking a dump.
before or after working out.

They tend to be as far off as 5% to 15% at any given time.

The impedance: will show me as being 24% fat
The calipers: will have me at 14% fat
Hydrostatic: (accurate) has me at 13.1%
Pod Pod: (accurate)
DXA: (accurate) most precise

As you can see, the calipers (even with my inexperienced use of them) is within 1% of my actual BF; while the impedance is not even close.

Follow the conversation on this thread:

http://www.eroids.com/forum/general/off-topic/body-fat-analyzer

gold standard for BF measurement is the bod pod. Google it. They are relatively cheap and easy to find. 20-40 bucks and accurate to within 2.5%. Much better than calipers and a great way to be truly honest with yourself. I was surprised mine was as high as it was because you could still see my six pack but bod doesn't lie and I had to adjust my diet. I was 8-10 % off of what I thought I though I was.

theyre shit. they base your bf of bmi which is a horrible way to determine bf. get some calipers.