Relative humidity (RH) is a percentage. In a humidor, it is the number people disagree about most. If it is too low, cigars dry out, crack, and burn hot. If it is too high, the draw becomes tight, the burn becomes uneven or goes out, and the risk of mold rises. Temperature matters too: warm, moist air is riskier than cool, moist air.
Commonly recommended ranges are about 65–72% RH. The old rule of “70 percent humidity at 70 degrees” is a starting point, not a requirement. Some storage advice for Cuban cigars prefers the mid-to-high 60s and a cooler room. This site does not choose between them. Pick a number in that range and keep it steady. See the humidor article.
Calibrate your hygrometer. An analog dial that has never been checked with a salt test cannot be trusted. See humidity control and hygrometers.