For a comparison as to what is considered normal, a growth chart is used that also takes into account the child’s age and gender. The National Center for Health Statistics offers a nationally accepted growth chart also knows as a height weight chart. With this informative chart, a child’s, weight, in ounces and pounds or grams and kilograms, are bases on the child’s age in weeks, months and years. Height or length, in inches or centimetres, is measured on any child under three years of age, while they are lying down. Only after the age of three is a child measured standing up. These measurements of height and weight are recorder and graphed up to twenty years of age. The circumference of the head is also monitored and taken by a tape measure which is wrapped around the head, above the eyebrows. These measurements can provide an early warning as to a possible medical problem. For example, within the first eighteen months of life, abnormal head growth can alert the doctor to a possible problem. Brain tumor, or hydrocephalus, water around the brain, are two causes of head circumference growth this seems to rapid. Growth this is to slow could be a sign of brain development or even early fusion of the skull bones.