In the beginning there were priests. Then Blizzard said "Let there be other classes!" Things have been a lot more complicated ever since. Fortunately, there is Spiritual Guidance, WoW.com's bi-weekly guide for priests. On Sundays you can enjoy discussion on discipline, holy, and healing in the company of Dawn Moore. We don't have cookies here, but only because we call them biscuits, and serve them with tea, sandwiches, and scones. Did you want one lump, or two?

A couple of months ago I found myself talking to a non-priest about the gems I had slotted on my character. He was of the understanding that disc priests wanted nothing but crit, and thought it was strange that I had gemmed straight spellpower on all my gear. Figuring he was behind on the times, I happily explained to him that I was using the standard gem set up for shield spamming disc priests, which works around the premise that if the majority of what we do is cast shields, then we should stack as much spellpower as possible in order to make our most used spell (Power Word: Shield) absorb more. This is the standard practice advised to shield spammers throughout the priest community, and I've advised it here on Spiritual Guidance before as well.

The non-priest still didn't understand though. He kept insisting "but crit ..." which inclined me to gently stroke back his hair and say "there there, poor little confused non-priest, it's all right." I allowed him his dignity though, and instead went on with my explanation. I told him that alternative stats like crit and haste didn't do much for shield spamming since Power Word: Shield can't crit, and Borrowed Time removes the necessity for haste since the talent carries us down to the 1 second GCD soft cap whenever we cast Power Word: Shield. The non-priest still didn't understand, so I explained to him that a disc priest's primary interest in crit was Divine Aegis, a talent which applies a second shield whenever one of your spells crits. "But shields don't crit," I reiterated. "The heal from the Glyph of Power Word: Shield can, but that would only add say ... 500 extra absorption from Divine Aegis. The spellpower is still better."

As I typed out those last words, they boomeranged back and hit me square in the face. Startled, I peeled the sans serif off my nose and and reexamined the limp letters in my hands. Suddenly I wondered, "is that really true?"

The question

After I pulled the last of the ink from my eyebrows, I quickly set to work at trying to figure out the math for my question. My stream of thinking went like this: The Glyph of Power Word: Shield causes each Power Word: Shield you cast to heal your target for 20 percent of the amount of the shield. If we say the the average absorb amount for Power Word: Shield is 10,000, then the glyph will heal our target for around 2,000 health. If the heal effect crits, then we'll heal our target for 150 percent of your heal, which is 3,000 health. But that critical heal from the glyph will also apply a Divine Aegis. The Divine Aegis will absorb damage equal to 30 percent of the critical heal, even if it overheals. So, if the crit heal from the glyph is 3,000, that means the Divine Aegis would absorb around. 900 points of damage.

I sat back and looked at my numbers. The numbers were inflated but still, I had never really considered just how much extra absorption Divine Aegis could do through Power Word: Shield. I never questioned the validity of spellpower stacking before. After all, I had come to the bubble spam scene late, pursuing a career in tank healing well into early Icecrown Citadel. When I did submit to the good of the raid, I just accepted the methods and shrugged off any benefit from crit as negligible. But now I started to wonder if crit and Divine Aegis had been accounted for in shield spammer throughput. How beneficial might it be to increase my Divine Aegis output as a shield spammer?

My thoughts wandered to the extra spellpower I had on my gear from gems and wondered what they did for me. I had 17 Runed Cardinal Rubies equipped, adding up to almost 400 spellpower. If I swapped those out for spellpower and crit gems, I could get an extra 3.7 percent chance to crit in exchange for about 200 spellpower. If I wanted to drop the spellpower completely and go with straight crit gems, I would be giving up that 400 spellpower for an extra 7.4 percent.

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