Not a problem Schook.
The chart is used by HVAC engineers (not me). Humidity at high temperatures is very hard to gage by feel.
If you read across the bottom of the chart (Dry Bulb Temp) first, find the temperature and then go up vertically until you intersect the curvy lines (RH%). Then follow the slanted lines upward and to the left until you get to the 100% RH upper left side of the chart. That is the Wet Bulb Temp, or the theoretical temperature at which rain would fall.
At 55% RH, the chart tops out around 107°F.
As you noted, the chart does go over 50% RH. It goes up to 100% RH, but not for the higher temperatures.
Flying in conditions that bad, should always be done with a hat, plenty of water, sunglasses and common sense.
At 100°F, the chart stops near 70% RH.
Note that the 90°F/90°RH point people back east speak of is on the chart and would truly be a miserable day.