How accurate are these?

The other day I was working out and one of the professors from upstairs came down with a bioimpedence bodyfat calculator. I was one where you entered your height weight age and sex. You then held the two handles and it would tell you your body fat.

I was wondering how accurate these things were because it said that I was at 9%. Should I trust these things. Nine probably sounds right and if anything it is high. I am 6' and about 195. Has anyone else ever used one of these things?

A lot of these digets work fine on normal people but the lower your body fat gets the less accurate they become...XXL