Now we use something called "Idle Up"

In position 1 on the switch, the throttle and collective are linked together.
Think of the throttle stick as a clock. With the stick at the 6'o clock position, the motor is at a dead stop, and there is 0 pitch in the blades.
As you move the throttle up towards 12 'o clock, head speed increases and positive pitch increases.

In position 2 (commonly referred to as idle up) The throttle is set at a specific RPM, and the stick controlls the collective.
At the 6'oclock position, full headspeed(throttle) is applied and full negative pitch is applied.
At mid stick position, hovering headspeed(throttle) is applied and 0 or "flat" pitch is applied.
At 12' o clock position, full headspeed(throttle) is applied and full positive pitch is applied.

Positive pitch = air blowing down.
Negative pitch = air blowing up.

So to get the heli inverted.

The pilot pulls it up into a hover by moving the throttle stick towards 12' o clock until the heli lifts off. Once he gets into a stable hover, then he flips the "idle up" switch.
He bumps the throttle towards 12' o clock to make the heli "leap" upwards a little, while applying forward cyclic. As the heli starts to nose over into inverted flight, the pilot moves the throttle stick towards 6'o clock to apply negative pitch. Once he comes back over to right side up flight, the pilot moves the throttle stick back towards the 12' o clock position to return to positive pitch.