meaning only good birds will produce those results. well fed on the correct diet and in good condition.
hobby incubators are a very good fun tool but can vary greatly between machines even, its just a case of getting it correct for the machine you have, some will always be better than others. im currently running 2 r-com pros, 1 definitely gets better results than the other although both are on auto and running the same eggs on same settings. 1 also uses alot more water than the other.
i did find that the brinsea type rockers (i ran several at the same time at busy times)benefited from