Here are the exact steps for finding the right spot to pinch

Here are the exact steps for finding the right spot to pinch, and taking an
accurate skinfold with the Accu Measure calipers
1. Holding the Accu measure in your right hand in "pinch-ready" position, reach
   across your body with your left hand and locate the proper skinfold site by
   taking your left index finger and putting it on the top of your right hip bone
   (That's the "Illiac crest). This is the anatomical landmark you must find before
   you take the measurement. Don't just grab randomly without locating the spot
   first - it's extremely important to grab the same place every time. One inch
   up, down, left or right and your measurements will be inconsistent.
2. Leaving your left index finger on the spot, take your left thumb and pinch the
   skinfold firmly between your left thumb and index finger.
3. Without letting go of the skinfold, clamp the caliper onto the middle of the
   skinfold using your right hand. As you close the caliper, the plastic slide-rule
   will move until the point where the Accu measure "clicks" – that's when you
   know your measurement is done. Then, release the caliper jaws and look at the
   calipers to see where the black line on the slide rule is pointing. That number is
   your lliac crest skinfold thickness in millimeters.
4. When you're just starting out, I recommend taking three measurements. If
   they're all the same, (i.e, 13, 13, 13) then your accuracy was good and that's
   your measurement. If they're close, take the average of the three (example,
   14, 13, 13.5 = average of 13.5 mm). If your measurements "all over the map"
   (19 mm, 11 mm, 15 mm), your technique is off and you need some practice!
   Don't give up - keep working at it.
5. Record the SINGLE measurement at the illiac crest once per week. Measure to
   the half of a millimeter: If the black line on the slide rule points to between 12
   and 13, write down 12.5 millimeters as your measurement.
6. You now have your skinfold thickness in millimeters. To translate that number
   into a body fat percentage, look at your skinfold interpretation chart. The chart
   that comes with the Accu measure caliper is fine, but to avoid making the chart
   huge and cumbersome, it only lists skinfolds within a 2 mm range. Therefore
   the original Accu measure chart may over or under estimate your body fat. I
   wanted more precision, so one day, I took it unto myself to crunch some
   numbers and improve the chart. My "expanded" Accu measure skinfold
   interpretation chart has taken the data from the original chart and extrapolated
   it to the half millimeter in skinfold thickness and it gives you a body fat