PIP: The growth charts used worldwide to measure infant weight do not quantify centile crossing and therefore cannot monitor weight gain. Velocity charts are impractical since they involve two charts and weight velocity has to be calculated for each pair of measurements. A new growth chart is described, designed for 4-week measurement intervals, which combines distance, velocity, and conditional references in one. It consists of conventional weight centiles complemented with extra lines called thrive lines, where the slope defines a cutoff for failure to thrive. Variability in the change in weight standard deviation score (SDS) over time depends only upon the correlation between the two measurements, which in turn depends upon age. A child's weight is plotted and joined to the previous weight 4 weeks earlier, then the slope of the line is compared with the slope of the nearest thrive line. If the child's slope is the smaller, weight gain is below the fifth centile. The chart's main weakness is that measurements need to be 4 weeks apart, which is often unrealistic. The chart is, however, robust to a range of measurement intervals if interpreted correctly. Its sensitivity and specificity under field conditions need to be assessed.