What that means is that with a high enough UMD you can cast scrolls of Heal or wands of Cure Light Wounds even though you are a rogue or sorcerer, you can equip Elvish race-restricted weapons as a Warforged or Chaotic alignment-restricted items as a Lawful character. With a high enough UMD you can essentially expand your character’s utility immensely.

If you are serious about accessing as many magical devices as possible especially as a non-magic-using class you will want to shoot for a buffed UMD score of 44, which is currently the highest ranked item in the game – the Scroll of Resurrection. However having a total UMD rank of 40 will still allow you to use basically everything else.

If you do not plan to use high-level scrolls or restricted items or if your overall character design will not feasibly allow it, a better method is to target the UMD Difficulty Check (DC) of the specific items you plan on using. It may turn out you really only need a total rank of 20.

To determine the UMD DC of an item, simply double its level and add 18. Or rather -

(item_level * 2) + 18 = DC

So the DC of old faithful, Wand of Cure Light Wounds, which is a level one item, is 20. So what does that mean? That number is the what you will make your UMD skill check against.

To successfully use this wand as, for example, a Rogue you would need to roll higher than 20 on a d20+UMD. If you are not familiar with dice shorthand that means you roll one 20-sided die and add your total UMD rank. What that also means, therefore, is that if you have a total UMD rank of 20 you will be able to use this wand 100% of the time without failure.

What makes up a character’s “total” UMD skill rank?

UMD is determined by adding the ranks you spend points on after leveling, your Charisma modifier, the Skill Focus: UMD feat and a very few rare items in game which have a UMD skill boost.

It is a primary skill of Rogues and Bards and a secondary skill for everyone else, meaning they will only spend one point to raise their UMD a rank while all other classes must spend two skill points.

Rogues and Rangers can temporarily boost UMD through their respective Action: Skill Boost enhancements. Humans get the same type of boost through the Human Versatility Bonus enhancement and Bards can get a boost to UMD via the Spellsinger enhancement (at level six). But other than that, UMD bonuses are pretty hard to come by, so if you are dedicated to having a high UMD, make sure to always reserve your skill points to keep it maxed for your level and consider assigning Skill Focus: UMD as one of your feats.

So if you decide to emphasize UMD in your DDO character build, keep this in mind. Sometimes it could be worth having the one-level splash of Rogue or Bard for this among their other talents.

Also keep in mind when designing your character, that if you play a class with casting abilities you already have access to wands and scrolls of spells your class has access to. As an example, even though as a Ranger you start at level 1 with no spells you will be able to use the Wand of Cure Light Wounds because it is one of your class spells you will later be able to cast.