I use a black PILOT super colour marker (permanent type) ULTRA FINE which I find works well.
There are kits available (google "chart corrections" to find them) These contain pens and stencils for about £35. The pens are red and violet (not sure why...some forumites will soon let us know I hope!)
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That Pilot pen looks good - is the ink waterproof ?
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Well i'm not sure it's "waterproof" but Iv'e just rubbed a wet finger over some Pilot pen writing on an Imray chart and it didn't smudge. So it seems to do the job OK.