I found something interesting on the forums that I hadn't seen before:

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Q u o t e:

Not familiar with Quarts and stopcast macros.
I use basic macros now for pyroblast opener/fireballs. Can you elaborate
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/stopcasting
/cast name_of_spell

When you start a cast on the client it does not start immediately upon the server. There is a certain amount of lag. When the spell finishes on the server, you are not immediately notified on the client. Again, there is a certain amount of lag involved. This means that your 3sec FireBalls may only end up being cast once every 3.5 seconds. This is ~15% nerf to your dps.

What Quartz does is color-code your cast bar so that you can visually identify the current amount of lag. By the time the cast bar reaches the "red zone" you could move, jump, (or issue the cmd /stopcasting) AND YOUR SPELL WOULD STILL COMPLETE because my the time the interrupt request reached the server it would have already finished.

Converting all your dmg spells into /stopcasting macros means that you don't have to move/jump/esc-key to perform early cancellation.

The reason Blizzard is looking into ways of defeating this lag issue in future patches is because if you want to compete at a high level, then you MUST use /stopcasting macros.......

So, in simple terms: You can inturrupt your casts using this addon and start casting another but the server will not recieve the inturrupt request until it thinks the cast has finished and will blast them anyway.

Some of you may already know about this but I found it interesting.

I checked out the addon Quartz and it has some pretty neat features for everyone actually. Description here, download here.

'course if the server DOESN'T think you're done casting, when you send the next spell in, the previous one is cancelled and you've lost the entire casting time. Need some timing to do it right. :)

That's what the quartz addon does. It figures out what the server latency is and adds a red area to the casting bar to tell you when you can cancel it.

But, yes, if you do it too early you bork yourself.

Bork!

Hmm, I've only used Quartz as just a regular replacement for the casting bar, and never paid much attention to the lag area. I'll look into that since I already have it installed and let you know how it works.

Thats cool that there is an add-on to try and help with casting but i really dont see the need for it.:D

I've been using if for a few days now, and really like it.....