Divination spells reveal the nature of items, the dungeon around you, and the unknown.
The following spellbooks teach you divination spells:
|Spellbook||Spell level||Direction||Relative probability||Probability conditional on price||Actions to read||Skill changes|
|Spellbook of detect monsters||1||non-directional||4.37%||15.0%||3||S|
|Spellbook of light||1||non-directional||4.58%||15.7%||3|
|Spellbook of detect food||2||non-directional||3.05%||12.8%||5||S|
|Spellbook of clairvoyance||3||non-directional||1.52%||16.5%||8|
|Spellbook of detect unseen||3||non-directional||2.03%||8.6%||10|
|Spellbook of identify||3||non-directional||2.03%||8.6%||14||S|
|Spellbook of detect treasure||4||non-directional||2.03%||16.7%||17||S|
|Spellbook of magic mapping||5||non-directional||1.83%||47.4%||37|
Spell failure rate and more powerful effects are the two main reasons to spend skill slots on divination.
Detect monsters, detect treasure, identify, and to a lesser degree detect food, become much more useful at skilled level. Good spellcasting classes will want to advance to skilled unless skill slots are at a premium. Expert and skilled levels have the same effects for all spells in this school, so there is usually no benefit to becoming expert.
If you have these spells, you will likely be casting them a lot. Therefore, basic skill is definitely worthwhile for the spell failure rates. Lesser spellcasters such as rangers and archeologists may sometimes want to become expert (or get a robe) to cast magic mapping, but as divination spells are rarely critical, even they are probably better off just sticking to skilled.
In SLASH'EM, the infinitely useful identify spell is increased in difficulty from level 3 to level 5. That makes it more compelling to advancing this skill to expert. Flame mages can gain expert, ice mages can gain basic.