At August's 6-month well check, he was coming up in the 0.56 percentile for weight by age and 0.11 percentile for weight by length. But he doesn't seem underweight, so we were confused. The charts they give us are converted to kg. I had a suspicion that perhaps the nurse was entering the ounces as a decimal of a pound. So when he weighed 12 lbs, 7 oz, he entered 12.7 pounds. That's not a huge difference, but when he weighed 13 lbs 13 ounces, that is a big difference from 13.13 pounds. I figured out the math and confirmed this is the exact error. So I brought it to their attention and had his chart corrected. He is still low on the percentile charts, but at least now it's accurate. I corrected the posts for 2-month and 4-month stats on this blog as well.
January 30, 2013 ~ 6 month stats
13 lbs 13 oz - 1.76 percentile
26.12 inches - 28th percentile
Weight-Length ratio: 0.77 percentile
This all means that of baby boys the same age, he weighs less than about 98% of them, and is longer than about 28% of them. Of baby boys the same length as August, he weighs less than over 99% of them. So we have another tall, thin one - just like Madelyn (although she was never this low on the charts).