There are accurate testing procedures and equipment, but you really need to follow the instructions. I can do caliper tests and compare to hand held digital body fat machines and be very close to the same.
If you want accurate, you need to get into the tub of water to do it correctly. Are they called underwater weighing, or DEXA or something like that. The closest one that I know of is about 30 minutes from me and not cheap.
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2007 Jamis Ventura Comp
2006 Jamis Explorer 2.0
2000 Specialized Hardrock (bought used)
Swim, Bike, Run and sounds like fun