No allowance was made for the size of eggs used. Large eggs are about 17% larger than medium, but the recipes seem tolerant of the natural variation of egg mass. The ratio of flour to milk seems more important.
Consistent details in recipes include that the oil or fat in the cooking tins must be very hot - almost smoking, and that opening the oven to inspect progress is detrimental.
I suppose I'll have to make a Yorkshire pudding now to see what the fuss is about. Is it supposed to be that -- flat?