Page "Double clutch" Paragraph 12

Conversely, in order to shift down, engine RPM must be increased while the gearbox is in neutral and the clutch is either engaged or disengaged.

This requires the driver to shift into neutral, apply throttle to bring the RPM up to a suitable speed, and finally shift into gear.

This operation can be very difficult to master, as it requires the driver to gauge the speed of the vehicle and throttle accurately.

Double clutching occurs if the clutch pedal is released while matching engine speeds in neutral and again engaged prior to shifting into the next gear.