Download the open source Guild Wars 2 Damage Meter (jaxnX) and measure your outgoing / incoming damage / heal.
Since damage meters are essential to optimize traits in almost any game and the developers of Guild Wars 2 decided to not support them by default, several people developed their own damage meter.
The problem with those solutions is, that they have to access game memory in some form, which is prohibited by the Terms of Service of GW2, what again makes them illegal.
That is what separates jaxnX from them.
If you have any questions left, feel free to ask at email@example.com
You have found bugs in the software?
Please send us a mail to firstname.lastname@example.org
You can also support our product by donating. It helps us improve the software for further recognition support.
jaxnX does not offend the Terms of Service of Guild Wars 2. It does not read from game memory.
Instead it uses Computer Vision techniques to read out numbers presented in the combat log by taking screenshots of the chat block periodically, converting pixels of the image into numbers and using the converted numbers for dmg / dps calculation.
The whole process happens in real time.