Yes it was 40%; not 50%, but it doesn't change the numbers much... Anyway I didn't say that Acashic everywhere was a good idea, just that it can pay for itself if you cast it from time to time on a high magic freq province (waste, swamp, "magic rich if marked on map..).
Manual searches don't cost gems but cost valuable mage-time and are a lengthy process, evreything has its pro and cons (hi Gandalf !
) and I usually use all methods - first "manual" searches, then magic, and possibly Acashic if I have the resources later on.