In August, I bought a Tanita digital scale with body fat % capability. The weight is dead on, compared to our other scale, but the body fat % reading has some quirks. You enter gender, age, height, and either default activity level or 'athletic'.
So, if I put in my correct stats and default, it says my body fat is like 13%. If I select 'Active' it says 6%. Neither one correct according to caliper measurements of 10.2% (January, 2009). So, I basically had to iterate on the height input to get something close - which meant entering my true height minus 1. inch for Active or adding 2 inches to my height for default.
I'm really just trying to see the trend vs. time, but it would be nice if the readings were more accurate per my correct height.