Acantha absolutely has a steady hand when he's not pretending to be terrified of everything (or seizing) and because he's trained all his life for this mission, he has worked hard to make his memory nearly perfect too. With a little practice writing by hand (admittedly, he's only ever typed before) he could accurately replicate any tablet he's had a chance to look at for a few minutes. With a lot of practice, he could replicate down to the original creator's 'handwriting' as it were.