1. Calculation Fundamentals and Unit Consistency
BMI is calculated as weight divided by height squared. In metric form, BMI = kg / m^2. In imperial systems, conversion factors are applied to maintain equivalent interpretation. Many user mistakes come from mixed units: entering centimeters where meters are expected, or pounds with metric height. A strong guide emphasizes normalization before calculation. If your calculator accepts both unit systems, explain each input path clearly and provide one conversion example so users can verify sanity before trusting output.
Even when arithmetic is correct, precision choices affect display quality. Round final BMI values consistently and avoid over precision that implies false accuracy. One or two decimal places are usually enough for interpretation. Include a note that small day to day weight fluctuations can change BMI marginally without changing practical health decisions. This helps users avoid reactive interpretation based on noise.