%% One of the best reads on an edge is named = Market Makers Edge by MS ,market maker Joshau Lukeman.And its much , much more than making money on the bid /ask. I ignore most of the outdated fractions, in that book -except 1/2[ 1/2 or 50 % seems still helpful sometimes].
Market Makers have an edge... don't they need it to be in business? Not something we retail screen jockeys can work for ourselves.