Except you don’t need to improvise in the case of an unreliable airspeed procedure. Just maintain pitch and thrust it works just fine. Then and only then a quick check at your GPS speed....Yeah if you want. Not required by Airbus QRH tho.
When I fly raw data departure, I always set 10 degrees pitch and CLB thrust and the speed always sit at 250kt +-5kt. It’s super accurate and very easy to remember the pitch/ thrust setting. At least approximately enough to fly 1 or 2 min safely to give time to the PM to find the accurate pitch and thrust setting without overspeeding or stalling.
Most of the time, If you do nothing the plane will keep flying perfectly fine. Relax and take your time.
