The chart is a map of all children
A growth chart plots the whole population: the 50th percentile line is the median child, the 3rd and 97th bracket the healthy extremes. Your child's point says where they are in that distribution — nothing more. Pediatricians look for a child's line running PARALLEL to the reference lines, wherever it sits on the page.
The two findings that matter
First: sustained percentile crossing — a child drifting from the 70th to the 30th across visits, in either direction. Second: velocity anomalies — growth slowing below age expectations. Both are trend findings; neither can be seen in a single measurement, which is why well-child visits exist on a schedule and home tracking works best at 6-month spacing.
The channel concept
Clinicians informally describe children as "growing in their channel" — a percentile band they follow consistently. A healthy child can live at the 5th percentile; the same child cannot healthily slide from the 5th to off-the-chart-low. The percentile calculators here give you the point; the velocity calculator gives you the slope; the pediatrician reads both together.