The plotted series is on the right. Seven major percentile lines are drawn — 3rd, 10th, 25th, 50th, 75th, 90th and 97th. Count the lines the child has crossed, and in which direction.
Corrected age is chronological age minus the number of weeks born before forty weeks. It is used for plotting growth and for judging development — and never for timing immunisations.
Correction is conventionally applied to weight and length for about two to three years, and to head circumference for about eighteen months.
One measurement decision per card — the instrument, the chart, or what the finding means.