[MagicRat]

Hi,
Welcome to AF

Sorry, I accidentally lost you pic. My fault and my apologies

First of all, you do not have to 'hold' the revs when shifting. You rev the engine a bit, then let the revs fall. When the revs fall to exactly the desired point, when you know the speed of both the input and output shafts are the same, you shift.

So how do you know? Through experience, based on road speed, the gear desired, engine pitch (sound) vibration, the 'feel' of the car.

Second, some cars, (not just race cars), especially old or high mileage ones simply downshift more smoothly and more quickly when double clutching. My '79 Mustang and '84 Supra do just this, especially when downshifting into first gear.