Very simple : read a few books (in English!) on the BoB. I read about 20.

To sum up, Dowding and Park were obviously right when they didn't want to engage all their fighter squadrons at the same time, which would have meant that they would have been back on the ground, refuelling and rearming, all at the same time too and the Huns would have had an excellent opportunity to catch and hit them on the ground in spite of AAA. Besides, it was similar within the Armée de l'Air in May-June : the last serviceable 2, 3 , 4 or 5 fighters of a Groupe de chasse, if the rest were not, were kept for protecting their own airfield (above all the precious aircraft, even undergoing repairs). Don't infer from this that French fighters were wiped out for it would be a serious error, but this situation did exist sometimes. The neighbouring Groupes de chasse were generally all right.

I think it happened only once during the BoB that there were no reserves left - within 11 Group but 10 and 12 Groups nearby also totalled hundreds of fighters, part of which could have been used in an emergency : on one occasion all 11 Group-squadrons were airborne, as can be seen in the film on the BoB*. Nevertheless they had not taken off all at the same minute but with differences of up to 30 minutes in certain cases I guess, so that some sqns were able to land, refuel and rearm before the others did, and take off again if necessary.

* This was on August 18 or September 15 I think.