The synoptic chart for any constant-pressure surface, usually containing plotted data and analyses of the distribution of, for example, height of the surface, wind, temperature, and humidity. Constant-pressure charts are most commonly known by their pressure value; for example, the 1000-mb chart (which closely corresponds to the surface chart), the 850-mb chart, 700-mb chart, 500-mb chart, etc. Compare constant-height chart; see mandatory level.