How does HealthWatch calculate Blood pressure percentiles for children?
Based on the "Blood Pressure Tables for Children and Adolescents" from National Heart, Lung, and Blood Institute.For more information on Blood Pressure Percentiles, visit Blood Pressure Tables for Children and Adolescents

How does HealthWatch estimate 10-year risk of having a heart attack?
Calculated using a point system as described in the Third Report of the National Cholesterol Education Program (NCEP) Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults (Adult Treatment Panel III). For more information on Estimating Your 10-year Risk of Having a Heart Attack and Identifying Metabolic Syndrome, go to High Blood Cholesterol That You Need to Know and visit the Live Healthier, Live Longer Web site.

How does HealthWatch evaluates underweight and overweight?
Based on BMI and waist.For more information on BMI calculations, visit BMI: Body Mass Index

I'm looking for the reference for the waist circumference percentiles for children.
I think it is from Fern¨¢ndez JR, Redden DT, Pietrobelli A, Allison DB. J Pediatr 2004;145:439-44. Here is a link: http://www.gghjournal.com/volume21/1/ab17.cfm