Double de-clutch:-
1st Gear to 2nd gear - Clutch down gear to neutral, clutch up still in neutral - set throttle to match transmission speed to engine rpm which is a little lower that before when changing up, clutch down then select second gear.
Going down a gear is much the same but you need to increase the engine speed. And some drivers will blip the throttle with their heel while braking with their toe to achieve this.
When you get good this takes as little time as a conventional gear change and maintains very smooth and progressive power delivery.
On modern cars with syncromesh some people argue that the DDC is no longer of value and others say that it is what proper drivers on a track do.
Why do it - its much smoother - when cornering at 100+ on a track a typical rough gearchange could upset the balance of a car.
On a drag strip where you just want to get the car to the top speed then the power change has a place but you still risk wheelspin and loss of traction with this brutal method.
I'm just really interested in the debate as to wether this method still has value today. I feel that it does on the track and it is a habit you can learn on the open road.