When I have a beard and maintain a neckline, I usually start from the middle and work my way to the sides. Getting it even is just a matter of taking your time. Also, a slightly uneven neckline will be totally unnoticeable to others so don't get too wrapped up in "perfection".

Stop trimming your moustache; greater glory awaits!
...but if you are going to trim, do it right, go pencil...
...then, of course, a nice copstache can be cool too...

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