Set 29.92 inches (1013 mb) on the altimeter, climb 2000 ft AGL, adjust airspeed to 65 knots, lower collective to full down, roll throttles to idle stops, maintain aircraft stable at 65 knots with collective full down, note fuel onboard, record outside air temperature, indicated altitude (pressure altitude) and indicated rotor rpm as you pass through 1000 feet above ground - perform a power recovery and return to base.
On the density chart locate recorded outside air temperature then run a vertical line from there up to the pressure altitude recorded at 1000 ft above ground then run a horizontal line left to read the resulting density altitude.
On the autorotation chart locate the density altitude value on the left side of the chart then run a horizontal line right to the weight the helicopter was at the time the auto rotation rotor rpm was recorded, then run a line straight down to find the required autorotation rotor rpm.